Johnson County area

Population and density of Johnson County

The Census Bureau estimates that 636,906 people lived in Johnson County on July 1, 2025. That ranks #113 of 3,222 county equivalents nationally and #1 of 105 in Kansas. Since the April 1, 2020 estimates base of 609,865, the population has grown by 27,041 (+4.4%), compared with +1.3% for Kansas as a whole.

With 473.6 square miles of land, that is 1,345 people per square mile (519 per km²), placing Johnson County #135 nationally for density and #1 in Kansas. The median county equivalent has 47 people per square mile; the Kansas median is 8.1. Put another way, there are about 0.476 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 Johnson County

20 incorporated places lie at least partly in Johnson County. Together they are home to 622,155 people (97.7%); the other 14,751 (2.3%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Overland Park city, with 203,677 residents in the county. The county seat, Olathe city, has 150,025 residents. Among places with at least 1,000 residents in 2020, Spring Hill city grew fastest since then (+36%).

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

Metropolitan area

Johnson County is a central county of the Kansas City, MO-KS Metropolitan Statistical Area. Its 14 county equivalents have 2,270,682 residents on 7,256.8 square miles of land; Johnson County accounts for 6.5% of the land and 28% of the residents. By combined land it ranks #25 of 393 metropolitan areas, and #31 by population. It belongs to the Kansas City-Overland Park-Kansas City, MO-KS Combined Statistical Area.

ZIP codes

35 ZIP Code Tabulation Areas have land in Johnson County; 32 of them have most of their land inside the county, and the others mainly cover neighboring areas.

6601366018660216602566030660316606166062660836608566202662036620466205662066620766208662096621066211662126621366214662156621666217662186621966220662216622366224662266622766251

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 Johnson County

Johnson County shares a land border with 6 county equivalents, including 2 in Missouri. It has more land than 3 of them. The largest neighbor is Cass County (696.6 mi²) and the smallest is Wyandotte County (151.6 mi²). Together with its neighbors, Johnson County forms a block of 3,421.7 mi² of land, of which it holds 13.8%.

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

Johnson County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.2 times as much. Kansas’s county land could hold about 173 areas the size of Johnson County.

Another way to picture it: the same land area would fill a square about 21.8 miles (35 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 Johnson County?

Johnson County has more land than 1,044 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 Johnson County at #2,245 nationally by total area, 67 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 1.3%, compared with a national county-equivalent median of 1.2% — 0.1 percentage points higher. 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 Johnson 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.