How Much Does a 401(k) Audit Cost in Illinois?

Fee ranges by plan size, and what the Illinois audit market looks like in plan year 2024 Form 5500 filings: how many plans are audited, by how many firms, at what plan size, and who does the most of it.

Last updated September 6, 2026 · Source data: plan year 2024 Form 5500 filings

How much does a 401(k) audit cost in Illinois?

A 401(k) audit in Illinois typically costs $8,000–$18,000 a year — the national range, since fees track plan size, not geography. Illinois’ median audited plan (397 participants) falls in the $10,000 – $18,000 band. In plan year 2024, 387 firms audited 3,540 plans sponsored in Illinois.

3,540Audited plans in IL

387Active audit firms

397Median plan size (participants)

4.9%Share of U.S. audited plans

Typical 401(k) audit fees for Illinois plans

Typical annual 401(k) audit fee ranges by plan size (editorial estimates)
Plan size	Typical fee range	What drives the range
100–249 participants	$8,000 – $14,000	Most first-time audits land here; single payroll and one recordkeeper keep scope tight.
250–499 participantsIL median plan: 397 participants	$10,000 – $18,000	More participant-level testing; still typically one fieldwork cycle.
500–999 participants	$13,000 – $25,000	Larger samples; often multiple payrolls or acquisitions in the mix.
1,000–4,999 participants	$18,000 – $40,000	Complexity-driven: mergers, employer stock, non-standard assets push the top of the range.
5,000+ participants	$30,000+	Multi-entity sponsors, 11-K filers, and hard-to-value assets; fees are bespoke.

Honest labeling: audit fees are not reported in a standardized, reliable field on Form 5500, so these ranges are editorial estimates informed by published fee surveys and engagement quotes — not outputs of our filing dataset, and not specific to Illinois. The market figures below are from the dataset. A first-year audit adds roughly 10–25%; an ERISA Section 103(a)(3)(C) election removes roughly 15–40%. See the national cost guide for the full list of fee drivers.

The Illinois audit market: the numbers behind a quote

Illinois employee benefit plan audit market, plan year 2024
Measure	Illinois	United States
Audited retirement plans (sponsor address in Illinois)	3,540	72,776
Audit firms with at least one engagement	387	3,956
Audited plans per active firm	9.1	18.4
Median audited plan size (participants)	397	357
Share of plans audited by the ten most active firms	44%	24%
Most active firm’s share of plans	6%	5%

National concentration is the share of all retirement plan engagements held by the ten largest firms nationally; the Illinois figure is the share of IL-sponsored plans audited by the ten most active firms in the state. State reflects the plan sponsor’s address, not the audit firm’s offices.

Illinois’ median is close to the national median of 357 participants, so the national fee framework applies without adjustment. The market is moderately concentrated: the ten most active firms audited 44% of Illinois’ plans, with the balance spread across 377 other firms — a mix of regional specialists and occasional auditors.

Rankings derived from U.S. Department of Labor Form 5500 filings, plan year 2024. Read the full methodology.

Most active 401(k) audit firms in Illinois

Firms ranked by audited retirement plan filings sponsored in Illinois, plan year 2024
#	Firm	IL plans audited	Share of state
1	Sikich CPA LLC	228	6.4%
2	CliftonLarsonAllen LLP	221	6.2%
3	Plante & Moran, PLLC	206	5.8%
4	Crowe LLP	155	4.4%
5	RSM US LLP	151	4.3%
6	Forvis Mazars, LLP	150	4.2%
7	Miller Cooper & Co., LTD	124	3.5%
8	Grant Thornton LLP	112	3.2%
9	Baker Tilly US, LLP	110	3.1%
10	Smith & Howard, PC	106	3.0%

Top 10 firms shown. Counts are retirement plan filings (401(k), 403(b), profit-sharing, and pension) whose sponsor address is in Illinois. Volume measures experience, not quality or price.

Rankings derived from U.S. Department of Labor Form 5500 filings, plan year 2024. Read the full methodology.

The full ranked directory, with market totals, is at 401(k) audit firms in Illinois. Each firm profile shows engagement counts, states served, opinion mix, and the firm’s largest audited plans.

How to get a fair 401(k) audit quote in Illinois

Quote on the same scope. Tell every candidate whether the plan will elect an ERISA Section 103(a)(3)(C) audit, how many payroll systems it runs, and whether it files Form 11-K. Otherwise the low bid is usually the narrow one.
Engage before spring. Nearly every Illinois plan is due July 31 or October 15; firms fill fieldwork calendars first-come, and engagements that start after Labor Day pay for the compression. See the deadline guide.
Shortlist by volume. Ask three to five firms from the table above, or from the state directory, and check each profile for client sizes comparable to yours. A Illinois office is optional — audits are performed under national standards from recordkeeper and payroll data — but demonstrated volume is not.
Deliver clean records. Reconciled census, dated remittances, SOC 1 reports, and the certification in hand before fieldwork are the cheapest fee reduction available. The document checklist lists everything the auditor will request.

Illinois 401(k) audit cost FAQs

Do 401(k) audits cost more in Illinois?

No systematic premium applies. Audit fees are driven by participant count, plan complexity, and record quality rather than the sponsor’s location, and most engagements are performed remotely. Illinois’ median audited plan had 397 participants in plan year 2024, versus 357 nationally, which places a typical Illinois plan in the $10,000 – $18,000 editorial fee band.

How many firms audit 401(k) plans in Illinois?

387 audit firms signed at least one audit of a retirement plan sponsored in Illinois in plan year 2024, covering 3,540 audited plans (4.9% of the U.S. total). The ten most active firms accounted for 44% of those plans; the rest were spread across 377 other firms.

Which firm audits the most 401(k) plans in Illinois?

Sikich CPA LLC audited 228 Illinois retirement plans in plan year 2024, the most of any firm and 6% of the state’s audited plans. CliftonLarsonAllen LLP (221) and Plante & Moran, PLLC (206) ranked second and third. Engagement volume signals experience, not quality; each firm profile shows opinion mix and client sizes.

401(k) audit cost in other states

Same fee framework, different market. Each page carries the state’s audited plan count, active firms, median plan size, and most active auditors from plan year 2024 filings.