Clark County is a county in Illinois, United States, along the Wabash River on the Indiana border, in the southeastern part of the state. It had a population of 15,455 at the 2020 census and covers 505 square miles (1,308 km2) centred near 39°20′N 87°47′W.
Marshall is the county seat, and its postal code is 62441. The county has three cities, one village, and dozens of unincorporated communities spread across fifteen civil townships. Clark County sits in the Central time zone.
Towns & Villages in Clark County
Clark County has four incorporated places — three cities and one village — plus roughly three dozen unincorporated communities, several of which are 19th-century hamlets that never grew past a crossroads store or a rail siding. In the table below, CDP marks a Census Designated Place and Unincorp. marks a community with no municipal government.
| Place | Type | Township | Pop. | ZIP |
|---|---|---|---|---|
| Marshall | City · seat | Marshall | 3,947 | 62441 |
| Casey | City | Casey | — | 62420 |
| Martinsville | City | Martinsville | — | 62442 |
| Westfield | Village | Westfield | — | 62474 |
| Dennison | Unincorp. | — | — | 62423 |
| West Union | Unincorp. | — | — | 62477 |
| Darwin | Unincorp. | Darwin | — | — |
| Melrose | Unincorp. | Melrose | — | — |
| Orange | Unincorp. | Orange | — | — |
| York | Unincorp. | York | — | — |
| Adenmoor | Unincorp. | — | — | — |
| Allright | Unincorp. | — | — | — |
| Castle Fin | Unincorp. | — | — | — |
| Choctaw | Unincorp. | — | — | — |
| Clark Center | Unincorp. | — | — | — |
| Clarksville | Unincorp. | — | — | — |
| Cleone | Unincorp. | — | — | — |
| Doyles | Unincorp. | — | — | — |
| Ernst | Unincorp. | — | — | — |
| Farrington | Unincorp. | — | — | — |
| Fox Run | Unincorp. | — | — | — |
| Golf Lakes | Unincorp. | — | — | — |
| Hogue Town | Unincorp. | — | — | — |
| Livingston | Unincorp. | — | — | — |
| McKeen | Unincorp. | — | — | — |
| Moonshine | Unincorp. | — | — | — |
| Moriah | Unincorp. | — | — | — |
| Neadmore | Unincorp. | — | — | — |
| Oak Point | Unincorp. | — | — | — |
| Oakcrest | Unincorp. | — | — | — |
| Oilfield | Unincorp. | — | — | — |
| Patton | Unincorp. | — | — | — |
| Snyder | Unincorp. | — | — | — |
| Walnut Prairie | Unincorp. | — | — | — |
| Weaver | Unincorp. | — | — | — |
| Weir | Unincorp. | — | — | — |
Darwin, on the Wabash River in the county’s northeast corner, was Clark County’s first seat of government before Marshall took over in 1838 — it is now a small unincorporated river settlement, not to be confused with any other Darwin nationally. The old list’s “Cumberland” entry has been dropped: no populated place of that name is verified inside Clark County, and it most likely reflected confusion with neighboring Cumberland County.
Townships
Clark County is divided into fifteen civil townships. Detailed 2020 township-level population counts were not available from the sources checked for this update, so only the county total (15,455) is confirmed; the county assessor’s or Census Bureau’s township tables can be checked for the exact per-township split.
| Township | Pop. (2020) | Main settlements |
|---|---|---|
| Marshall | — | Marshall (county seat) |
| Casey | — | Casey |
| Martinsville | — | Martinsville |
| Westfield | — | Westfield |
| Darwin | — | Darwin |
| York | — | York |
| Melrose | — | Melrose |
| Orange | — | Orange |
| Anderson | — | rural, no incorporated place |
| Auburn | — | rural, no incorporated place |
| Dolson | — | rural, no incorporated place |
| Douglas | — | rural, no incorporated place |
| Johnson | — | rural, no incorporated place |
| Parker | — | rural, no incorporated place |
| Wabash | — | runs along the Wabash River; no incorporated place |
ZIP Codes
- 62441 — Marshall (also serves the surrounding Marshall Township)
- 62420 — Casey (also serves the surrounding Casey Township)
- 62442 — Martinsville (also serves the surrounding Martinsville Township)
- 62474 — Westfield
- 62423 — Dennison
- 62477 — West Union
Clark County’s smaller unincorporated communities do not have their own ZIP code; mail for places like Darwin, Melrose, and York is routed through the nearest post office town above.
Geography
Clark County sits on the rolling till plains of southeastern Illinois, cut by the Wabash River along its eastern edge and drained inland by the Embarras River and several smaller creeks. The county is mostly farmland — corn and soybeans on the uplands, with wooded bottomland along the Wabash and Embarras valleys.
Clark County borders Edgar County to the north, Coles County to the northwest, Cumberland County to the west, Jasper County to the southwest, and Crawford County to the south. Across the Wabash River to the east lies Vigo County, Indiana, and Sullivan County, Indiana, borders the southeast corner.
Demographics
Clark County had 15,455 residents at the 2020 census, spread over 501 square miles of land — a density of about 31 people per square mile. Marshall, the county seat, is the largest community at 3,947 residents; Casey is the county’s second-largest incorporated place, though a verified 2020 figure for it was not available from the sources checked for this update. Median household income in the county runs below the Illinois median of $80,306, consistent with a rural, agriculture-dependent county.
Economy & Local Life
Farming remains the backbone of the local economy, alongside county-government and school-district employment centered in Marshall. Casey is known nationally for its collection of oversized roadside attractions — including a giant wind chime, mailbox, rocking chair, and golf tee, several recognized by Guinness World Records — built by local businessman Jim Bolin’s “Big Things in a Small Town” project, which draws Route 40 and I-70 travelers off the highway into the town’s small shops and cafes.
History
Clark County was organized in 1819, carved out of Crawford County, and named for George Rogers Clark, the Revolutionary War officer who led the 1778–79 campaign that secured the Illinois Country for Virginia. Darwin, on the Wabash River, served as the first county seat before the government moved to the more centrally located Marshall in 1838. The county’s early settlement followed the Vincennes Trace and the Wabash River, which carried the first flatboat trade between Illinois farms and downstream markets.
Getting There
Interstate 70 crosses the county east–west through Casey and Marshall, running parallel to the older US Route 40. Illinois Route 1 runs north–south through Marshall and Martinsville.
- Terre Haute, Indiana — about 15 miles east
- Charleston, Illinois — about 25 miles northwest
- Effingham, Illinois — about 35 miles southwest
- Paris, Illinois — about 20 miles north
The nearest commercial airport is Terre Haute Regional Airport, just across the Indiana line.
Frequently Asked Questions
Where is Clark County, Illinois?
It is in southeastern Illinois, on the Wabash River along the Indiana border, roughly 15 miles west of Terre Haute, Indiana.
What is the population of Clark County?
Clark County had a population of 15,455 at the 2020 census.
How big is Clark County?
The county covers 505 square miles (1,308 km2), of which about 3.4 square miles is water.
What is the county seat of Clark County?
Marshall is the county seat.
How many towns are in Clark County?
The county has four incorporated places — the cities of Marshall, Casey, and Martinsville, and the village of Westfield — plus around three dozen unincorporated communities.
What ZIP codes are in Clark County?
The main ZIP codes are 62441 (Marshall), 62420 (Casey), 62442 (Martinsville), 62474 (Westfield), 62423 (Dennison), and 62477 (West Union).
Why is Casey, Illinois famous?
Casey is known for its collection of Guinness-recognized “world’s largest” roadside attractions, part of a local revitalization project that draws visitors off Interstate 70.
More counties in this state: Towns and villages in Illinois.