Marion County area

Population and density of Marion County

The Census Bureau estimates that 28,525 people lived in Marion County on July 1, 2025. That ranks #1,534 of 3,222 county equivalents nationally and #38 of 115 in Missouri. Since the April 1, 2020 estimates base of 28,526, the population has declined by 1 (−0%), compared with +1.9% for Missouri as a whole.

With 436.9 square miles of land, that is 65 people per square mile (25 per km²), placing Marion County #1,319 nationally for density and #29 in Missouri. The median county equivalent has 47 people per square mile; the Missouri median is 31. Put another way, there are about 9.8 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 Marion County

3 incorporated places lie at least partly in Marion County. Together they are home to 20,679 people (72.5%); the other 7,846 (27.5%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Hannibal city, with 16,521 residents in the county (the city extends into 1 other county). The county seat, Palmyra city, has 3,649 residents. Among places with at least 1,000 residents in 2020, Palmyra city grew fastest since then (+1%).

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

Metropolitan area

Marion County is a central county of the Hannibal, MO Micropolitan Statistical Area. Its 2 county equivalents have 38,969 residents on 906.7 square miles of land; Marion County accounts for 48.2% of the land and 73.2% of the residents. By combined land it ranks #209 of 542 micropolitan areas, and #335 by population. It belongs to the Quincy-Hannibal, IL-MO Combined Statistical Area.

ZIP codes

10 ZIP Code Tabulation Areas have land in Marion County; 5 of them have most of their land inside the county, and the others mainly cover neighboring areas.

63401634386343963440634436345463456634616346363471

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 Marion County

Marion County shares a land border with 6 county equivalents, including 2 in Illinois. Each of them has more land than Marion County. The largest neighbor is Adams County (855.2 mi²) and the smallest is Ralls County (469.8 mi²). Together with its neighbors, Marion County forms a block of 4,246.7 mi² of land, of which it holds 10.3%.

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

Marion 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. Missouri’s county land could hold about 157 areas the size of Marion County.

Another way to picture it: the same land area would fill a square about 20.9 miles (33.6 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 Marion County?

Marion County has more land than 902 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 Marion County at #2,368 nationally by total area, 48 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 Marion 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.