Illinois wetlands regulations sit at the intersection of federal and state law: most private construction, drainage, or fill work in a wetland requires a Section 404 permit from the U.S. Army Corps of Engineers and a Section 401 water quality certification from the Illinois EPA, while the state’s own Interagency Wetland Policy Act of 1989 mainly governs projects carried out by state agencies. Unauthorized wetland damage can run tens of thousands of dollars per day in penalties, and the permitting process typically takes months. Knowing which rules apply to your parcel — before you break ground — is the whole game.
What Counts as a Wetland Under Illinois Law
Under the Interagency Wetland Policy Act of 1989, a wetland is land with a predominance of hydric soils (soils usually saturated with little or no free oxygen) that is flooded or saturated by surface or groundwater frequently enough to support plants adapted for wet conditions.1Illinois General Assembly. Illinois Compiled Statutes 20 ILCS 830/1-6 – Definitions Areas created or restored through mitigation projects also count, even when not all three characteristics (hydric soils, water-tolerant plants, wet conditions) are simultaneously present.
An owner’s informal impression of what looks like a wetland often doesn’t match the technical definition. Flat, seasonally soggy land that doesn’t look like a marsh can still qualify. That gap between intuition and legal definition is where compliance problems start, because the definition is what determines whether a permit is needed.
Who Regulates Wetlands in Illinois
Two systems overlap. The federal Clean Water Act covers most private development. The state Interagency Wetland Policy Act (20 ILCS 830) is narrower than its name suggests: it directs state agencies to preserve wetlands when planning construction or land management, and when adverse impacts on state-supported projects are unavoidable, the agency must develop a wetland compensation plan approved by the Illinois Department of Natural Resources.2Illinois General Assembly. Illinois Compiled Statutes 20 ILCS 830/3-1 The Act does not directly regulate private landowners the way many people assume.
For a private project, the gatekeepers are the U.S. Army Corps of Engineers, which issues permits under Section 404 of the Clean Water Act for discharging dredged or fill material into wetlands, and the Illinois EPA, which must certify under Section 401 that the project will not violate state water quality standards.3U.S. Environmental Protection Agency. Permit Program under CWA Section 404 No federal permit issues without that state certification, which effectively gives Illinois EPA veto power over federally permitted wetland projects.4Illinois Environmental Protection Agency. 401 Water Quality Certification Program
The Corps evaluates individual permits through a public interest review and the Section 404(b)(1) Guidelines. Illinois EPA’s review focuses on potential water quality impacts and includes an antidegradation assessment. A wetland fill project in Illinois faces scrutiny from at least two agencies before construction can begin.
How Sackett v. EPA Narrowed Federal Coverage
The 2023 Supreme Court decision in Sackett v. EPA changed which wetlands fall under federal jurisdiction. Before Sackett, the EPA asserted authority over wetlands with a “significant nexus” to navigable waters, a broad standard that reached many isolated or loosely connected wetlands. The Court rejected that test.5Supreme Court of the United States. Sackett v. EPA (May 25, 2023)
Under the new standard, a wetland falls under federal jurisdiction only if it has a continuous surface connection to a relatively permanent body of water that is itself connected to traditional interstate navigable waters — meaning the line where water ends and wetland begins must be difficult to draw. Wetlands separated from covered waters by a berm, road, or dry gap no longer qualify for federal protection under Section 404.
Over a million acres of Illinois wetlands may have lost federal protection under the narrower standard. Illinois does not currently have comprehensive state legislation that fills this gap for private development. Some counties and municipalities have their own wetland ordinances, but coverage is uneven. If you are developing land with wetlands that appear isolated, get a current jurisdictional determination from the Corps rather than assuming the old rules still apply, and check your local county and municipal codes.
The Permit Process for Private Projects
If your project requires filling, dredging, or otherwise discharging material into a jurisdictional wetland, you will need both a Section 404 permit from the Corps and a Section 401 water quality certification from Illinois EPA.
What You Have to Show
An application must demonstrate three things in sequence: that you have taken steps to avoid wetland impacts entirely, that you have minimized whatever impacts cannot be avoided, and that you will compensate for the remaining unavoidable damage.3U.S. Environmental Protection Agency. Permit Program under CWA Section 404 A permit cannot be issued if a less damaging practicable alternative exists.6U.S. Environmental Protection Agency. Wetland Regulatory Authority Applicants who treat the alternatives analysis as a formality tend to get their applications sent back.
Illinois EPA’s 401 Certification
To submit a valid certification request to Illinois EPA, you need a completed federal permit application (Corps Form ENG 4345 or the Joint Application Form) and written confirmation from the Corps that an individual Section 401 certification is required.4Illinois Environmental Protection Agency. 401 Water Quality Certification Program Illinois EPA has one year from receipt of a valid request to act. The agency may request additional technical information during review and may schedule public hearings.
Fees and Costs
The Section 401 certification fee is $350 or one percent of the gross value of the proposed project, whichever is greater, up to a maximum of $10,000 per application.7Illinois Environmental Protection Agency. Water Quality Certification Fees The certification cannot be granted without payment. State agencies and school districts are exempt.
Budget separately for a professional wetland delineation, the field study that maps wetland boundaries on your site. Costs typically run $3,500 to $10,000 or more depending on the property’s size and ecological complexity.
Public Hearings
Both the Corps and Illinois EPA may hold public hearings on individual permit applications. Neighbors, environmental groups, and other stakeholders can raise concerns, and the agencies can impose conditions based on what surfaces, including compensatory mitigation beyond what the applicant originally proposed.
Farming, Drainage, and USDA Rules
Farming and wetland regulation intersect in ways that catch many Illinois landowners off guard. Federal law exempts some farming activities from Section 404 permitting but imposes strict conditions on others, and a separate USDA program governs eligibility for federal farm benefits.
Section 404 Farming Exemptions
Normal, ongoing farming activities on established agricultural land — plowing, seeding, cultivating, and harvesting — are exempt from Section 404 permitting, as are construction and maintenance of farm ponds, irrigation ditches, and maintenance (but not new construction) of drainage ditches.8eCFR. 40 CFR Part 232 – 404 Program Definitions; Exempt Activities Not Requiring 404 Permits The critical word is “established.” Converting new land into farming use does not qualify, and neither does any activity that creates drainage structures significant enough to modify a wetland, stream, or lake.
Minor drainage incidental to crop production, such as maintaining upland ditches and tiles, is also exempt when it does not discharge material into waters of the United States. Expanding an existing tile system to drain a wetland that was previously too wet to farm crosses the line from exempt maintenance into regulated activity. That distinction is where most agricultural enforcement actions originate.
USDA Wetland Conservation Compliance
Even where a Section 404 permit is not required, farmers who receive USDA program benefits face a separate set of rules. The wetland conservation provisions of the Food Security Act of 1985 require producers to avoid farming converted wetlands or converting wetlands for crop production as a condition of eligibility for most USDA programs.9Natural Resources Conservation Service. Conservation Compliance for Wetlands
You can continue to farm areas where drainage existed before December 23, 1985, and can maintain that drainage to its original scope. Any expansion that increases production or lets the wetland be farmed in additional years is a potential violation. If you know or suspect wetlands exist on your farm, you may work those areas when conditions permit but cannot drain, fill, or clear them. Converting a wetland after the 1985 date means the land cannot be used for commodity crops without losing USDA program eligibility.
Farmers who cannot avoid impacting a wetland have two options: mitigate by restoring or creating replacement wetlands in the same watershed, or request a minimal effect determination from NRCS. Getting a wetland determination before starting any new drainage project is the easiest way to avoid an expensive compliance problem later.
Penalties for Unauthorized Wetland Work
Skipping the permit is costly. Under the Illinois Environmental Protection Act, anyone who violates the Act, its regulations, or a permit condition faces civil penalties of up to $100,000 for the violation plus up to $25,000 for each day the violation continues.10Illinois General Assembly. Illinois Compiled Statutes 415 ILCS 5/42 – Civil Penalties For violations tied to NPDES water discharge permits, the cap is $25,000 per day. Penalties can be ordered by the Illinois Pollution Control Board or by a court.
Federal penalties are steeper. Effective for penalties assessed on or after January 8, 2025, the maximum civil penalty under Section 404 is $68,445 per day for each violation.11eCFR. 40 CFR Part 19 – Adjustment of Civil Monetary Penalties for Inflation The EPA can also require removal of the discharged material and full restoration of the damaged site, or if that is not feasible, compensatory mitigation at another location.12US EPA. How Enforcement Actions Protect Wetlands under CWA Section 404
Restoration ordered as part of an enforcement action often costs far more than the fines. Failing to comply invites injunctions and additional litigation. Getting a permit up front, even when the process is slow and expensive, is much cheaper than cleaning up after an enforcement action.
Mitigation Banking When Impacts Are Unavoidable
When a project unavoidably destroys wetland acreage, the developer must offset the loss. Mitigation banking is the most common route for private development in Illinois.
A wetland mitigation bank is a site where wetlands have been restored, created, or preserved in advance, generating “credits” that developers can purchase to satisfy their mitigation obligations. Illinois has multiple active mitigation banks overseen by the U.S. Army Corps of Engineers across several districts, including banks in the Rock Island, Chicago, Louisville, and St. Louis Corps districts.13U.S. Army Corps of Engineers. Wetland Mitigation Banks in Illinois – Rock Island District Credits are evaluated using functional assessment procedures that measure the ecological value being replaced, and prices are negotiated between buyer and bank operator.14NRCS. Let’s Talk Wetland Mitigation Prices vary by service area and availability; costs of $40,000 or more per acre are not unusual nationally.
USDA program participants who lack on-site mitigation options can also purchase credits from an approved bank to compensate for converted wetlands. The requirement is the same whether the project is a subdivision, a highway widening, or a farm drainage expansion: the wetland functions lost must be replaced.
Property Tax Reduction for Keeping Wetlands Intact
Illinois offers a meaningful property tax incentive for landowners who maintain wetlands. Under the Conservation Stewardship Law (35 ILCS 200, Division 16), unimproved land, a category that explicitly includes wetlands, qualifies for reduced assessment if the owner commits to a conservation management plan approved by IDNR.15Illinois General Assembly. Illinois Compiled Statutes 35 ILCS 200 – Property Tax Code, Conservation Stewardship Law
The land must be five or more contiguous acres of undeveloped wetland, woodland, prairie, or similar land not used for any residential or commercial purpose that materially disturbs it. In all counties except Cook County, qualifying land is assessed at just five percent of its fair cash value. The special valuation does not apply to land already assessed as farmland, valued as open space, or certified as a nature preserve.
Buying or Selling Land With Wetlands
Wetlands on a property can restrict what you build, require expensive permitting, and reduce developable acreage. The Illinois Residential Real Property Disclosure Report asks sellers about flooding, floodplain location, and flood insurance, but it does not include an explicit question about the presence of wetlands. A seller who knows the land is in a floodplain must disclose that, but there is no specific box to check for wetlands.
For buyers, relying on the seller’s disclosure is not enough. Before closing on rural or undeveloped land, a wetland delineation performed by a qualified environmental consultant is the only reliable way to know what you are buying. The consultant maps wetland boundaries using the Corps of Engineers’ methodology, examining soils, vegetation, and hydrology. Costs typically run $3,500 to $10,000 or more depending on the property’s size and complexity.
For commercial developers, wetland due diligence is not optional. Many Illinois counties require a wetland determination as part of the development permitting process, and lenders financing development projects routinely require environmental assessments that include wetland mapping. Discovering a wetland after site plans are drawn and financing is committed is one of the most expensive surprises in Illinois land development.