Building permits, zoning and land rules in Washington County, Illinois

Washington County requires a building permit for construction under county jurisdiction, including agricultural buildings¹. Farm structures qualifying under Section 4-13 of the county zoning code have no filing fee; that exemption does not waive the building permit³. The published schedule lists no fee for structures under 150 square feet and a $100 fee for structures at or above 150 square feet³. Obtain a Certificate of Zoning Compliance before construction begins². Illinois has had statewide building codes since 2025; locally adopted residential codes must regulate structural design at least as stringently as the International Residential Code (IRC), while jurisdictions without an adopted code follow the state’s residential framework⁸. Ask the county or municipal code official which code governs the project⁸.

The Washington County Zoning Office is the contact for county building permits and zoning administration¹. The office is at 125 W. St. Louis St. in Nashville, can be reached at (618) 327-4800 extension 345, and is open weekdays from 8am to 4pm¹. Inside a city or village, confirm whether that municipality issues the parcel’s building permit⁴. County applications require applicant/owner authorization, a legal description or E-911 address or parcel number, and a site plan with measurements from property lines and other buildings². A noncompliant proposal may need an interpretation, variance, zoning amendment, or special-use permit². We could not confirm a building-inspection schedule, county-adopted code edition, or certificate-of-occupancy process; ask the office issuing the building permit^2,8.

Washington County zoning governs unincorporated land¹. Published classifications include Agricultural, Commercial, Industrial, Interchange, and R-1, but the available provisions do not establish a complete district schedule; ask the Zoning Office for the parcel’s district and applicable use and dimensional rules³. Centralia, a city reaching into Washington County but mainly in Marion County, administers its own zoning⁹. Septic regulation remains with IDPH and any participating local health agency⁵. Commercial solar facilities have setbacks of 150 feet from nonparticipating dwellings and occupied community buildings, and 50 feet from nonparticipating property lines and public road rights-of-way³. Those commercial solar setbacks do not establish house setbacks; we could not confirm ordinary residential setbacks, minimum lot or dwelling size, or general height limits, so ask the Zoning Office before choosing a house site³.

Illinois IDPH regulates private sewage systems serving Washington County; local health agencies may review plans under local ordinances or as IDPH agents⁵. Illinois requires septic plan approval from IDPH or the applicable local authority before construction, plus at least 48 hours’ notice before installation or modification begins¹⁰. Contact the Washington County Health Department first to identify the reviewing authority and septic application for the address^5,11. Only 3.2% of county soils are rated without severe limits for a conventional drain field, making a site evaluation an early purchase priority¹². Eligible surface-discharging systems also face Illinois EPA authorization, inspection, monitoring, and reporting requirements¹³. Private-well construction, modification, or sealing needs a permit from IDPH or an approved local health department before work begins¹⁴.

We could not confirm a Washington County rule allowing or prohibiting long-term RV occupancy, temporary camping on private land, or tiny-home occupancy; ask the Washington County Zoning Office about the proposed use¹. For unincorporated land, ask the Washington County Zoning Office about the district, duration, and utility arrangement; inside a city or village, ask the municipal zoning office⁴. Illinois campground licensing does not answer whether one household may occupy an RV on its own parcel¹⁵. A tiny home involving construction under county jurisdiction still needs a building permit, and its proposed residential use must fit the applicable zoning district^1,3. Septic plan review remains an IDPH or participating local-health-agency question regardless of which office handles building permits or zoning⁵.

1. Determine whether the parcel is unincorporated or inside a city or village, then ask the zoning authority for the district, allowed use, setbacks, and any variance or special-use need^3,4.

1. Contact the Health Department to identify who reviews the septic plan, and complete that review before fixing the house location^5,11.

1. If the property needs a private well, obtain the required well permit before work begins⁶.

1. For a county-administered parcel, submit the Certificate of Zoning Compliance application with authorization, parcel identification, and a measured site plan².

1. Obtain the building permit from County Zoning or the applicable city or village^1,4.

1. Ask the issuing office which inspections and final approvals apply, because we could not confirm that schedule².

Start with jurisdiction and buildability. Confirm whether the parcel is unincorporated or inside a municipality, identify the applicable zoning district, and get written answers on the dwelling, setbacks, access, and parcel division^3,4. Test the proposed sewage area early: only 3.2% of Washington County soils are rated without severe limits for conventional drain fields¹². The terrain is broadly workable, with 95.2% of land at a slope of 15% or less, but that does not replace a site survey or drainage review¹². Check whether floodway authorization is needed; regulated rural floodways generally include streams draining at least 10 square miles¹⁶. The effective property-tax rate is 1.8%, with a median annual bill of $2,766¹².