County Maps US

Marion County, Missouri

A county in Missouri, ranked 38 of 115 by population.

CountyFIPS 29127

Within Missouri
Marion County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Palmyra, the county seat, located via the 2025 Census Gazetteer.

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Population
28,525
+45 (+0.2%) since 2020
Land area
436.9
square miles. A further 1.7% of the total area is water
Population density
65.3
people per square mile, computed rather than published
County seat
Palmyra
Seat of county government.
Established
1826
199 years ago
Largest city
Hannibal city
Population 16,521 for the whole place, which extends beyond this county.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Marion County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Marion County, Missouri from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 800 by 586 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Marion County ranks

Position among the 115 counties of Missouri, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn MissouriNationally
Population28,52538th of 1151,493rd of 3,144
Land area436.9 sq mi97th of 1152,320th of 3,144
Population density65.3 per sq mi29th of 1151,240th of 3,144
Median household income$62,90343rd of 1151,807th of 3,143

Full data for Marion County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population28,525Vintage 2025 Population Estimates
Population in 202028,480Vintage 2025 Population Estimates
2020 estimates base?28,526Vintage 2025 Population Estimates
Land area436.9 sq mi2025 Gazetteer Files
Water area7.4 sq mi2025 Gazetteer Files
Total area444.3 sq mi2025 Gazetteer Files
Population density?65.3 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$62,903American Community Survey 2020-2024 5-Year Estimates
Median home value$162,000American Community Survey 2020-2024 5-Year Estimates
Median age39.6American Community Survey 2020-2024 5-Year Estimates
Households11,323American Community Survey 2020-2024 5-Year Estimates
Housing units12,917American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
-16
377 births, 393 deaths
Net migration
+132
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 6 areas bordering Marion County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Ralls CountyMissouri24 mi10,444
Lewis CountyMissouri22 mi9,879
Shelby CountyMissouri20 mi5,870
Adams CountyIllinois16 mi64,267
Monroe CountyMissouri7.0 mi8,959
Pike CountyIllinois6.6 mi14,231

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 115 counties of Missouri

Open the interactive Missouri county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.