ADU Pass
Will County
ADU Pass helps homeowners in Will County, Illinois navigate the permit paperwork for building an accessory dwelling unit. We cover 20 cities and 32 ZIP codes in this county.
Map
County ADU details
County ADU ordinance
Will County, Illinois - 696,000 residents in the south-southwest exurban Chicago area - regulates accessory dwelling units in unincorporated territory through the Will County Zoning Ordinance, administered by the Will County Land Use Department. Will is a fast-growing exurban county with substantial unincorporated territory; incorporated cities include Joliet (largest), Bolingbrook-portion, Romeoville, Plainfield, Crest Hill, Lockport, Frankfort, Mokena, New Lenox, Tinley Park-portion, Channahon, Wilmington. Each incorporated municipality sets its own ADU rules under home-rule authority where applicable.
Code citations:
State-floor overlay: Illinois has not enacted statewide ADU preemption.
Adopting body: Will County Board
County permitting (unincorporated parcels)
Will County issues building permits for parcels in unincorporated territory through its development services / planning department, with separate review tracks for zoning conformance, building-code compliance, on-site sewage where applicable, floodplain compliance, and addressing. Inside incorporated municipalities, city departments handle their own permits; the county's authority is geographically limited to unincorporated territory. An ADU permit application is typically processed as a residential building permit with a zoning verification step against the county's ordinance for the parcel's zoning district.
Process overview: Typical workflow: (1) jurisdictional verification (parcel confirmed in unincorporated Will County, not inside city limits or extra-territorial jurisdiction); (2) zoning verification against the county ordinance; (3) building-code plan review against the adopted state building code; (4) site-plan, septic (where applicable), and floodplain review; (5) issuance, construction with inspections, and certificate of occupancy.
Impact fees: Will County permit fees are itemized at intake. Counties in Illinois commonly do not levy municipal-style impact fees on residential additions in unincorporated areas; verify current fee schedule at the development-services counter.
County assessor
The Will County property assessor / equalization office maintains parcel-level assessment records for all real property in Will County. ADU additions are typically captured as improvements to the host parcel via shared permit data with the building department. Illinois property-assessment rules govern annual revaluation cycles, homestead or principal-residence caps where applicable, and the procedures for protesting an appraisal.
Assessment policy: Improvement value for an ADU is added to the parcel record on the next regular revaluation cycle. Homestead / principal-residence caps where applicable shield the existing structure from rapid valuation increases but do not exempt new improvement value.
County overlays (2)
Will County administers flood-hazard, and (where mapped) coastal, wildland-fire, historic, and airport overlays that shape ADU project feasibility. The most consistent overlay across the county is FEMA NFIP floodplain regulation; other overlays apply to specific geographies inside the county.
- FEMA NFIP Special Flood Hazard Areas in Will County — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; cost impact on the project is often material.
- Historic districts and individually-listed historic resources
Illinois state — ADU law and programs
State financing programs
Illinois does not operate an ADU-specific statewide loan, grant, or forgivable-loan program. The Illinois Housing Development Authority (IHDA) is the state's housing finance agency and administers a robust portfolio of homebuyer products: Access Forgivable, Access Deferred, Access Repayable down-payment-assistance variants, the IHDA Mortgage first-mortgage product, and the federal Low-Income Housing Tax Credit allocation. The 2025 IHDA Access Home program offers DPA equal to 6% of purchase price up to $15,000. None target ADU construction directly; an ADU-bearing primary residence on an Illinois lot can qualify for the underlying mortgage when other criteria are met.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.