How do I know which meridian my Illinois county uses?

In general: southern Illinois counties below roughly the 38th parallel (Alexander, Union, Johnson, Pope, Hardin, Gallatin, White, Edwards, Wabash, and neighboring counties) use the Second Principal. Central and northern counties use the Third Principal. Northwestern counties bordering the Mississippi above the Illinois River mouth — Jo Daviess, Carroll, Whiteside, and Rock Island — use the Fourth Principal.

Why does Illinois have three principal meridians?

Multiple meridians were established in Illinois in the early 1800s to allow simultaneous survey work across the territory rather than sequentially extending a single control line. Federal survey administrators assigned different survey crews to different meridians to accelerate the opening of land for settlement. The result is a practical multi-meridian legacy that requires meridian identification for every description.

Can I convert Illinois descriptions for Chicago suburban properties?

Yes. Chicago suburban properties in Cook, DuPage, Lake, Kane, Will, and McHenry counties trace back to Third Principal Meridian descriptions in their original patents and early deeds. Enter the underlying PLSS description to identify the section and quarter section before researching the platted subdivision that was later created from that land.

How are Illinois coal lease descriptions formatted?

Coal leases in southern Illinois reference Second or Third Principal Meridian PLSS descriptions with specific aliquot-part subdivisions for the leased mineral tract. A typical coal lease description looks like: N2 SE 12 8S 3W 3rd Meridian. Enter this description to map the leased mineral tract and verify its acreage and county location.

Illinois PLSS Converter — Section Township Range to GPS

Convert Illinois Public Land Survey System (PLSS) land descriptions to GPS coordinates using the Second / Third / Fourth Principal system.

Convert Illinois Land Descriptions

Enter a Illinois PLSS land description to get GPS coordinates instantly.

Example: NE 27 8N 9E 3rd Meridian

Open the converter

Understanding Illinois's PLSS System

Illinois carries the distinction of being one of the earliest PLSS states and the only state surveyed under three distinct principal meridians. The Second Principal Meridian governs the southern portion of the state, with its initial point established in 1805 near Vincennes, Indiana. The Third Principal Meridian — established in 1805 at a point on the Ohio River in present-day Hardin County — controls central and northern Illinois, including the Chicago metropolitan area and the productive agricultural counties of the Illinois River valley. The Fourth Principal Meridian governs the northwestern corner of the state, particularly the counties bordering the Mississippi River above the mouth of the Illinois River.

The multi-meridian structure of Illinois is a legacy of the rapid nature of early PLSS expansion. Federal survey administrators in the early 1800s established multiple meridians in the Old Northwest to enable simultaneous survey work in different regions rather than waiting for a single control line to be extended across the entire territory. In practice, county location is usually sufficient to identify the meridian: southern Illinois uses the Second Principal; central and northern Illinois uses the Third Principal; the northwest river counties use the Fourth Principal.

Illinois was transformed by its early surveys. The Illinois and Michigan Canal corridor — surveyed and granted to Illinois by Congress in 1827 — was defined entirely by Third Principal Meridian PLSS descriptions and drove Chicago's emergence as a commercial center. The agricultural counties of central Illinois sit on some of the deepest and most fertile prairie soils in the world, and the PLSS grid imposed on them in the 1820s and 1830s still governs every farmland transaction, drainage district assessment, and USDA program enrollment in the state today.

Principal Meridians

Second Principal Meridian Third Principal Meridian Fourth Principal Meridian

Common Use Cases in Illinois

Who converts Illinois PLSS descriptions — and why.

Corn Belt Farmland Transactions

Illinois is among the top three corn and soybean producing states. Farmland sales, cash rent agreements, agricultural lending, and conservation easement programs all reference PLSS legal descriptions for every parcel. Buyers, sellers, lenders, and FSA offices rely on accurate GPS conversions to verify acreage and confirm field boundaries in one of the nation's most active agricultural land markets.

Chicago Metro Suburban Development

The Chicago metropolitan area's suburban fringe continues to expand into formerly agricultural land described in Third Principal Meridian PLSS terms. Subdivision plats, annexation petitions, and title searches in Cook, DuPage, Kane, Will, and McHenry counties trace back to original GLO quarter-section descriptions that must be accurately located before development can proceed.

Drainage District Management

Illinois has one of the most extensive drainage district systems in the country, covering millions of acres of agricultural land. Drainage assessments, tile easements, and outlet agreements are tied to PLSS parcel descriptions. Converting these descriptions to GPS helps drainage engineers, contractors, and district trustees manage infrastructure and plan improvements.

Coal and Mineral Rights

Southern Illinois sits over the Illinois Basin, one of the most significant coal-producing regions in the country. Coal leases, surface rights agreements, and oil production units in the basin reference Second and Third Principal Meridian PLSS descriptions. GPS conversion supports mineral rights title work, lease mapping, and regulatory filings with the Illinois Department of Natural Resources.

Industries: AgricultureReal EstateMining

How to Convert Illinois Legal Descriptions

Three steps from legal description to GPS coordinates.

Enter your Illinois legal description with the meridian

Type or paste your description and include the meridian designation — this is especially important in Illinois. A northern Illinois description reads: NE 27 8N 9E 3rd Meridian. A southern Illinois description reads: SW 14 7S 5W 2nd Meridian. A northwest Illinois description reads: NW 3 22N 5E 4th Meridian. The meridian is the key to accurate conversion in a three-meridian state.

Confirm the county and region on the map

The converter plots the parcel on an interactive map. Given the three-meridian system, a wrong meridian designation can place the parcel many miles from its true location. The map check is the fastest way to catch meridian errors before they propagate into documents or field work.

Export for your workflow

Download coordinates as CSV, KML, or GeoJSON. Illinois agricultural users commonly import into precision agriculture platforms and FSA portal tools; real estate professionals export to county GIS viewers; drainage engineers export to civil engineering software for district planning.

Processing an Illinois county farmland database, a drainage district parcel inventory, or a coal rights portfolio spanning multiple meridians? Batch conversion handles any number of Second, Third, or Fourth Principal Meridian descriptions from a single CSV upload.

Learn about batch conversion

Frequently Asked Questions

Common questions about Illinois PLSS descriptions and conversion.

Illinois uses three principal meridians: the Second Principal Meridian (southern Illinois), the Third Principal Meridian (central and northern Illinois, including Chicago), and the Fourth Principal Meridian (northwestern river counties). Always include the meridian designation when entering Illinois descriptions to ensure accurate conversion.