Buying Land in Illinois: What the State Controls Before a County Gets Involved

County zoning applies only outside cities and villages -- and forecloses township zoning where it exists

Illinois county zoning authority comes from the Counties Code, specifically 55 ILCS 5 Division 5-12, which lets a county board regulate and restrict the location and use of structures and land -- but only in unincorporated territory. A zoning ordinance adopted by a city, village, or incorporated town supersedes county zoning entirely inside that municipality's corporate limits, so a parcel just outside a small Illinois town can be governed by a completely different rulebook than one a mile down the road that's already inside the city line.

The detail that surprises buyers coming from Ohio or Michigan: Illinois townships do not compete with counties for zoning authority the way townships in those states do. Township zoning in Illinois is authorized separately under 60 ILCS 1, Article 110 of the Township Code -- but Section 110-5 of that Article states plainly that it "does not apply in any county in which a county zoning ordinance or resolution is in effect," and that a county zoning ordinance adopted after a township already zoned itself supersedes that township ordinance. In other words, county zoning wins by default. Since 55 ILCS 5 zoning is in effect in most of Illinois's larger and more populous counties, independent township zoning under Article 110 is the exception, not a co-equal system -- it survives only in the relatively few townships, in relatively few counties, where the county itself has chosen not to zone.

That doesn't mean townships have no voice. Illinois has roughly 1,426 townships across 85 of its 102 counties (the other 17 counties use a commission form of government with no townships at all), and where a township has its own plan commission, Illinois law gives it a real, if narrow, role inside the county's zoning process: under 55 ILCS 5/5-12007, if a township plan commission (in a county under 600,000 population) formally objects in writing to a proposed county zoning ordinance or amendment affecting unincorporated land in that township, the county board cannot adopt it except by a three-fourths supermajority vote of the full board. That's an objection-and-override mechanism layered inside county zoning, not a separate township zoning code running in parallel.

For a buyer, the practical takeaway is to call the county planning/zoning department first, not the township. If the county tells you it has no zoning ordinance, then ask the township directly whether it has adopted its own zoning under Article 110 -- that's the only scenario where township zoning actually governs. See our national guide to zoning for the general process once you know which office controls.

Septic: state standards from IDPH, permitting through the local health department

Illinois regulates septic systems -- what state law calls "private sewage disposal systems" -- under the Private Sewage Disposal Licensing Act (225 ILCS 225). The Illinois Department of Public Health (IDPH) sets the technical design, siting, and construction standards statewide through the Private Sewage Disposal Code (77 Ill. Admin. Code 905), covering systems with no surface discharge (conventional septic tanks and seepage fields) as well as certain systems that discharge limited treated effluent.

Actual permitting and plan review, though, happens locally. IDPH counts roughly 90 local health departments across Illinois that review private sewage system applications and issue permits, either under their own local ordinance (which can meet or exceed the state minimums, but not fall below them) or acting as IDPH's designated agent where no local ordinance exists. In practice, that means the site and soil evaluation, the permit application, the fee, and the inspection all happen through your target county's health department -- the state code sets the floor, but the county office is who you're actually dealing with. See our national guides to perc tests and septic systems for the general process.

Water rights: reasonable-use riparian doctrine, with a registration threshold for high-capacity wells

For surface water, Illinois follows the common-law "reasonable use" riparian doctrine rather than a prior-appropriation permit system: a landowner along a river, stream, or non-navigable lake may make reasonable use of the water, with what counts as reasonable weighed against the needs of other riparian owners on the same water body, and no landowner may divert, dam, or pollute the flow in a way that unreasonably harms others downstream. This is common law developed through Illinois court decisions rather than a single comprehensive statute, so a dispute typically turns on case-specific facts rather than a fixed rule.

Groundwater withdrawal in Illinois is governed by the Water Use Act of 1983 (525 ILCS 45), which codifies a "rule of reasonable use" for groundwater and separately requires registration for larger users. A "high-capacity well" -- defined as any well (or combination of wells on one property) capable of withdrawing 100,000 gallons of water in a 24-hour period, roughly 70 gallons per minute -- must be registered, with the owner reporting withdrawal data annually through the Illinois Water Inventory Program (IWIP), which the Illinois State Water Survey (part of the University of Illinois Prairie Research Institute) administers under the Act. Most single-family domestic wells fall well under that threshold and require no registration; a buyer planning large-scale irrigation, a bottling operation, or another water-intensive commercial use should check projected withdrawal against the 100,000-gallon figure.

Separately, the Illinois Department of Natural Resources' Office of Water Resources (IDNR-OWR) administers a different permitting program that reaches many rural parcels: a floodway construction permit is required for work within a mapped floodway, or for work affecting a stream with a drainage area over roughly 1 square mile in urban/urbanizing areas or 10 square miles in rural areas. This is a construction-in-the-floodway permit, distinct from the groundwater registration above, and is worth checking early for any parcel near a mapped stream or river.

What this page does not tell you

Everything above is the state-level layer. Whether your target county has adopted zoning at all, what its specific unincorporated-area zoning districts and setbacks allow, whether a township within that county retains its own zoning under the narrow Article 110 exception, and your county health department's specific septic fees, soil-evaluation scheduling, and site requirements are all determined locally and are not standardized across Illinois. See our national guides to zoning, perc tests, and septic systems for how those local conversations typically go.