Buchanan County area

Population and density of Buchanan County

The Census Bureau estimates that 83,540 people lived in Buchanan County on July 1, 2025. That ranks #712 of 3,222 county equivalents nationally and #15 of 115 in Missouri. Since the April 1, 2020 estimates base of 84,800, the population has declined by 1,260 (−1.5%), compared with +1.9% for Missouri as a whole.

With 408.3 square miles of land, that is 205 people per square mile (79 per km²), placing Buchanan County #635 nationally for density and #10 in Missouri. The median county equivalent has 47 people per square mile; the Missouri median is 31. Put another way, there are about 3.1 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 Buchanan County

8 incorporated places lie at least partly in Buchanan County. Together they are home to 72,464 people (86.7%); the other 11,076 (13.3%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is St. Joseph city, with 71,001 residents in the county.

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

Metropolitan area

Buchanan County is a central county of the St. Joseph, MO-KS Metropolitan Statistical Area. Its 4 county equivalents have 119,170 residents on 1,655.7 square miles of land; Buchanan County accounts for 24.7% of the land and 70.1% of the residents. By combined land it ranks #193 of 393 metropolitan areas, and #339 by population. It belongs to the Kansas City-Overland Park-Kansas City, MO-KS Combined Statistical Area.

ZIP codes

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

644016443964440644436444464448644546448464490645016450364504645056450664507

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 Buchanan County

Buchanan County shares a land border with 6 county equivalents, including 2 in Kansas. It has more land than 1 of them. The largest neighbor is Andrew County (432.6 mi²) and the smallest is Doniphan County (393.5 mi²). Together with its neighbors, Buchanan County forms a block of 2,925.7 mi² of land, of which it holds 14%.

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

Buchanan County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.5 times as much. Missouri’s county land could hold about 168 areas the size of Buchanan County.

Another way to picture it: the same land area would fill a square about 20.2 miles (32.5 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 Buchanan County?

Buchanan County has more land than 747 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 Buchanan County at #2,514 nationally by total area, 39 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 1.7%, compared with a national county-equivalent median of 1.2% — 0.5 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 Buchanan 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.