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Interview guides · Hennepin County, Minnesota

Hennepin County, Minnesota Software Engineer Interview Guide

Hennepin County, Minnesota Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at Hennepin County plays a pivotal role in delivering essential services to over 1.2 million residents. Unlike traditional tech firms, engineering here is driven by public impact. You will be responsible for developing, maintaining, and optimizing the digital infrastructure that powers everything from public health initiatives and social services to public safety and transportation systems. The work is both high-stakes and highly rewarding. As a Software Engineer, you are not just writing code; you are building the tools that social workers use to help families, that residents use to access property records, and that the county uses to manage massive infrastructure projects. This role requires a blend of technical expertise and a deep commitment to the community, as your solutions directly influence the efficiency and accessibility of local government.

This guide is scoped to a Software Engineer candidate at Hennepin County, Minnesota.

Focus areas

  • Technical skill demonstration
  • Language proficiency (listening, speaking, reading, writing)
  • Behavioral interview skills

The Hennepin County, Minnesota interview process

Hennepin County, Minnesota candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

Begins with a phone call with an HR recruiter or a pre-recorded video interview focusing on basic qualifications and motivation.

What to demonstrate

  • Begins with a phone call with an HR recruiter or a pre-recorded video interview focusing on basic qualifications and motivation
  • Depth in Technical skill demonstration

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Assessment

Candidates complete online technical tests and language assessments to ensure a baseline of proficiency.

What to demonstrate

  • Candidates complete online technical tests and language assessments to ensure a baseline of proficiency
  • Depth in Technical skill demonstration

How to prepare

  • Answer aloud and timed: "How do you handle a situation where you are given a task you don't fully understand?"
  • Answer aloud and timed: "What is your preference for working inside an office versus working remotely or in the field?"

Behavioral Assessment

Candidates participate in interviews with hiring managers and potential teammates, often conducted via Microsoft Teams or in person.

What to demonstrate

  • Candidates participate in interviews with hiring managers and potential teammates, often conducted via Microsoft Teams or in person
  • Depth in Technical skill demonstration

How to prepare

  • Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
  • Re-read the description of the behavioral assessment above and write down what you would ask to confirm before it.

Where candidates lose points

Research the County Mission

Familiarize yourself with the Hennepin County strategic plan. Showing that you understand the county’s goals (like disparity reduction) will set you apart.

Prepare for the Panel

You may be interviewed by 3 to 5 people at once. Have stories ready that appeal to different perspectives—one for the technical lead, one for the project manager, and one for the HR representative.

Be Specific About "Implementation

When asked about your experience, don't just say you "worked on a project." Explain your specific contributions, the tools you used, and the eventual outcome.

Dress Professionally

Even for virtual interviews, Hennepin County maintains a professional standard. Business casual is generally the expected attire.

Ask About the Team Structure

Use your turn to ask questions to show interest in how the IT department is organized and how they handle cross-departmental collaboration.

Questions & practice

"What is your preference for working inside an office versus working remotely or in the field?"

Medium · Behavioral & Experience

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

"How do you ensure your code is secure when handling sensitive user data?"

Medium · Technical & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

"Describe a complex technical problem you solved recently. What was your approach?"

Medium · Technical & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

"How do you stay current with new technologies, and how do you decide when to apply them to your work?"

Medium · Technical & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

  1. One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
  2. Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
  3. State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
  4. Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

  • A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
  • Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Replace offset paging on the resource feed with keyset

Easy · keyset pagination · composite index · sort order

resource holds resource_id, tenant_id, owner_user_id, title, body_ref, version, status ('draft','active','archived','deleted'), created_at, updated_at, deleted_at, with an index on (tenant_id, status, updated_at DESC, resource_id DESC). The listing endpoint returns active resources for one tenant, newest update first, 50 per page, today with LIMIT 50 OFFSET n. Tenants reach page 400 and rows are created while they read. Write the keyset query, define what the cursor carries and how it is encoded, and say which part of the index each predicate uses. Assume PostgreSQL 16.

Approach

  1. Name the two failures separately. OFFSET 20000 makes the server produce and discard 20,000 rows, so page cost grows with depth rather than with page size. Independently, any write that changes how many rows sort above the offset moves the window between two fetches, and the direction decides which anomaly you get: an insert lands at the head of updated_at DESC and pushes already-returned rows down past the boundary, so they are returned a second time; a delete above the offset, or a row whose updated_at is bumped above the cursor, pulls rows up and one is never returned at all. Nothing in the response reveals either.
  2. Write the seek: WHERE tenant_id = $1 AND status = 'active' AND (updated_at, resource_id) < ($2, $3) ORDER BY updated_at DESC, resource_id DESC LIMIT 50. The row-value comparison is one index range rather than a disjunction, and both columns are NOT NULL, which is what makes that comparison well defined.
  3. Map each predicate onto the index: tenant_id and status are equality on the leading columns, (updated_at, resource_id) is the range, and the ORDER BY matches the index order so no Sort node appears and the scan stops after 50 rows. The DESC in the definition only matters for mixed directions — a plain ascending btree on the same columns is read backwards for this query.
  4. Put both sort columns in the cursor and nothing the client can tamper with into another tenant: base64 of (updated_at, resource_id), validated server-side, with tenant_id taken from the principal.

Follow-up

  • The client asks for 'jump to page 400'. What do you offer instead, and what does the honest version cost?
  • Sort order becomes user-selectable across four columns. How many indexes is that, and which would you refuse to add?

"Explain the difference between a monolithic architecture and microservices in the context of a government age

Medium · Technical & Problem Solving

"Explain the difference between a monolithic architecture and microservices in the context of a government agency."

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Cache the tenant listing feed with a bounded staleness window

Easy · caching · cache invalidation · keyset pagination

GET /v1/resources returns one tenant's resources ordered by updated_at DESC, 20 per page, at 14k requests/second peak against a 120 ms p99. The table carries the index (tenant_id, status, updated_at DESC, resource_id DESC) and writes land on the primary at 1.2k/second. Design the read path: the pagination contract, the cache key and value, what a write invalidates, and the staleness a user can observe. State the request rate that actually reaches the database, and the one repopulation race that deleting on write does not close.

Approach

  1. Settle the pagination contract first, because it decides what is cacheable. OFFSET makes the database produce and discard the skipped rows, so page 500 costs five hundred pages of work, and rows inserted between two fetches shift across the boundary and are skipped or repeated with nothing in the response to reveal it. The cursor is the row value of the last row returned: WHERE tenant_id = $1 AND status = $2 AND (updated_at, resource_id) < ($3, $4) ORDER BY updated_at DESC, resource_id DESC LIMIT 21. That is a row-value comparison, not updated_at < $3 AND resource_id < $4, which is a different and wrong predicate.
  2. Confirm the index actually serves it: equality on the two leading columns, then a range on the pair that follows in exactly the index's sort order, so the plan is an index scan that touches 21 entries with no sort node. Requesting 21 to return 20 is how has_more is answered without a count. resource_id is not decoration - updated_at is not unique, and without the tie-break two rows sharing a timestamp at a page boundary are the skip that keyset pagination was adopted to remove.
  3. Key the cache on every value the predicate reads: tenant_id, status, cursor and page size. A key that omits tenant_id is a cross-tenant disclosure, and no test running against a single tenant's data will show it.
  4. Be honest that a write does not invalidate one key. An update moves its row to the head of the ordering, so it invalidates the first page and every cursor page whose range spans the row's old and new position, which is not enumerable. Cache the first page per (tenant_id, status) - that is where the traffic is - with a short TTL, invalidate it on write, and serve deep cursor pages uncached from a replica, since each is already a 21-row index scan and they are rare.

Follow-up

  • The tenant writes and immediately lists. What does it see, and what is the smallest change that makes its own write visible without sending all 14k requests/second to the primary?
  • A tenant has 4 million resources and a client walks every page nightly. What does that do to the cache hit rate, and should that traffic share this path at all?

"What is your process for debugging a production issue under a tight deadline?"

Medium · Technical & Problem Solving

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Hennepin County, Minnesota candidates report.

Day 1 — Map the Hennepin County, Minnesota loop

  • Write out the reported sequence: Initial Screening, Technical Assessment, Behavioral Assessment.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

Day 2 — Work Technical skill demonstration

  • Spend the session on Technical skill demonstration, which Hennepin County, Minnesota candidates report being tested on.
  • Write one worked example in Technical skill demonstration and time yourself on it.

Deliverable: One timed worked example in Technical skill demonstration.

Day 3 — Work Language proficiency (listening, speaking, reading, writing)

  • Spend the session on Language proficiency (listening, speaking, reading, writing), which Hennepin County, Minnesota candidates report being tested on.
  • Write one worked example in Language proficiency (listening, speaking, reading, writing) and time yourself on it.

Deliverable: One timed worked example in Language proficiency (listening, speaking, reading, writing).

Day 4 — Work Behavioral interview skills

  • Spend the session on Behavioral interview skills, which Hennepin County, Minnesota candidates report being tested on.
  • Write one worked example in Behavioral interview skills and time yourself on it.

Deliverable: One timed worked example in Behavioral interview skills.

Day 5 — Answer out loud: Behavioral & Experience

  • Answer aloud, timed: "Tell us about a time you failed on a project. What did you learn?"
  • Answer aloud, timed: "Describe your experience working in a team environment. What role do you typically take?"

Deliverable: Spoken answers to 2 reported Behavioral & Experience question(s), under time.

Day 6 — Answer out loud: Technical & Problem Solving

  • Answer aloud, timed: "How do you ensure your code is secure when handling sensitive user data?"
  • Answer aloud, timed: "Describe a complex technical problem you solved recently. What was your approach?"

Deliverable: Spoken answers to 2 reported Technical & Problem Solving question(s), under time.

Day 7 — Dry run for Hennepin County, Minnesota

  • Run one full mock under time, then write down the two questions you most want to ask your interviewers.

Deliverable: A completed timed mock and two questions to ask.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

"Tell us about a time you failed on a project. What did you learn?"

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

"Describe your experience working in a team environment. What role do you typically take?"

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

"How do you handle a situation where you are given a task you don't fully understand?"

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

"Walk us through a successful project you led from start to finish."

Medium · Behavioral & Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?