Piatt County area

Population and density of Piatt County

The Census Bureau estimates that 16,791 people lived in Piatt County on July 1, 2025. That ranks #2,051 of 3,222 county equivalents nationally and #62 of 102 in Illinois. Since the April 1, 2020 estimates base of 16,684, the population has grown by 107 (+0.6%), compared with −0.8% for Illinois as a whole.

With 439.2 square miles of land, that is 38 people per square mile (15 per km²), placing Piatt County #1,789 nationally for density and #60 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 17 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Piatt County

9 incorporated places lie at least partly in Piatt County. Together they are home to 11,554 people (68.8%); the other 5,237 (31.2%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Monticello city, with 6,080 residents in the county. Among places with at least 1,000 residents in 2020, Monticello city grew fastest since then (+2.3%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Piatt County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Piatt County is an outlying county of the Champaign-Urbana, IL Metropolitan Statistical Area. Its 3 county equivalents have 239,979 residents on 1,920.9 square miles of land; Piatt County accounts for 22.9% of the land and 7% of the residents. By combined land it ranks #164 of 393 metropolitan areas, and #204 by population. It belongs to the Champaign-Urbana-Danville, IL Combined Statistical Area.

ZIP codes

16 ZIP Code Tabulation Areas have land in Piatt County; 10 of them have most of their land inside the county, and the others mainly cover neighboring areas.

61813618186183061839618426185161853618546185561856618756188261884619136192961936

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Piatt County

Piatt County shares a land border with 6 county equivalents. It has more land than 3 of them. The largest neighbor is McLean County (1,183.2 mi²) and the smallest is Moultrie County (336 mi²). Together with its neighbors, Piatt County forms a block of 4,349.3 mi² of land, of which it holds 10.1%.

How big is Piatt County compared with U.S. states?

Piatt County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.4 times as much. Illinois’s county land could hold about 126 areas the size of Piatt County.

Another way to picture it: the same land area would fill a square about 21 miles (33.7 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Piatt County?

Piatt County has more land than 915 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Piatt County at #2,390 nationally by total area, 83 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 0.1%, compared with a national county-equivalent median of 1.2% — 1.1 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Piatt County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.