Marion County is a county in the U.S. state of Iowa. As of the 2020 census, the population was 33,414. The county seat is Knoxville. It is named for Francis Marion, a brigadier general from South Carolina in the American Revolutionary War.

According to the U.S. Census Bureau, the county has a total area of 571 square miles (1,480 km), of which 555 square miles (1,440 km) is land and 16 square miles (41 km) (2.8%) is water.

• Iowa Highway 5
• Iowa Highway 14
• Iowa Highway 92
• Iowa Highway 163
• Iowa Highway 316

• Jasper County (north)
• Mahaska County (east)
• Monroe County (southeast)
• Lucas County (southwest)
• Warren County (west)

Historical population

Census	Pop.	Note	%±
1850	5,482		—
1860	16,813		206.7%
1870	24,436		45.3%
1880	25,111		2.8%
1890	23,058		−8.2%
1900	24,159		4.8%
1910	22,995		−4.8%
1920	24,957		8.5%
1930	25,727		3.1%
1940	27,019		5.0%
1950	25,930		−4.0%
1960	25,886		−0.2%
1970	26,352		1.8%
1980	29,669		12.6%
1990	30,001		1.1%
2000	32,052		6.8%
2010	33,309		3.9%
2020	33,414		0.3%
2023 (est.)	33,770		1.1%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2018

The 2020 census recorded a population of 33,414 in the county, with a population density of 58.4743/sq mi (22.5770/km). 96.24% of the population reported being of one race. 91.15% were non-Hispanic White, 0.87% were Black, 2.09% were Hispanic, 0.21% were Native American, 1.20% were Asian, 0.06% were Native Hawaiian or Pacific Islander and 4.41% were some other race or more than one race. There were 14,073 housing units, of which 13,145 were occupied.

The 2010 census recorded a population of 33,309 in the county, with a population density of 60.1018/sq mi (23.2054/km). There were 13,914 housing units, of which 12,723 were occupied.

As of the census of 2000, there were 32,052 people, 12,017 households, and 8,532 families residing in the county. The population density was 58 people per square mile (22 people/km). There were 12,755 housing units at an average density of 23 units per square mile (8.9 units/km). The racial makeup of the county was 97.46% White, 0.42% Black or African American, 0.19% Native American, 1.03% Asian, 0.04% Pacific Islander, 0.22% from other races, and 0.64% from two or more races. 0.80% of the population were Hispanic or Latino of any race.

There were 12,017 households, out of which 33.00% had children under the age of 18 living with them, 61.20% were married couples living together, 6.90% had a female householder with no husband present, and 29.00% were non-families. 25.60% of all households were made up of individuals, and 11.90% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.02.

In the county, the population was spread out, with 25.30% under the age of 18, 10.20% from 18 to 24, 26.50% from 25 to 44, 22.10% from 45 to 64, and 15.90% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 98.60 males. For every 100 females age 18 and over, there were 95.80 males.

The median income for a household in the county was $42,401, and the median income for a family was $50,052. Males had a median income of $36,460 versus $25,573 for females. The per capita income for the county was $18,717. About 5.20% of families and 7.60% of the population were below the poverty line, including 8.70% of those under age 18 and 10.80% of those age 65 or over.

The population ranking of the following table is based on the 2020 census of Marion County.

† county seat

Rank	City/Town/etc.	Municipal type	Population (2020 Census)
1	Pella	City	10,464
2	† Knoxville	City	7,595
3	Pleasantville	City	1,676
4	Melcher-Dallas	City	1,195
5	Bussey	City	387
6	Harvey	City	236
7	Hamilton	City	119
8	Swan	City	76
9	Marysville	City	44

• 
  Marion County farmer with mule-drawn wagon, about 1926
• 
  Two Iowa farm boys riding a pony, about 1937
• 
  Iowa farm boy riding hog, about 1941
• 
  Farm house and barn yard near Pleasantville, 1957
• 
  Cows in farm pasture, 1957
• 
  Farmer getting coal, December 1957
• 
  Farm barnyard
• 
  Farm barnyard and silo, 1960

United States presidential election results for Marion County, Iowa

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	12,663	65.84%	6,178	32.12%	391	2.03%
2016	10,962	61.53%	5,482	30.77%	1,372	7.70%
2012	9,828	55.57%	7,507	42.44%	352	1.99%
2008	9,256	54.34%	7,421	43.57%	355	2.08%
2004	9,990	59.83%	6,574	39.37%	132	0.79%
2000	8,358	58.01%	5,741	39.85%	309	2.14%
1996	6,100	46.74%	5,978	45.80%	974	7.46%
1992	6,062	44.79%	5,531	40.87%	1,940	14.34%
1988	5,914	45.65%	6,922	53.44%	118	0.91%
1984	7,259	53.24%	6,313	46.30%	62	0.45%
1980	6,665	49.30%	5,490	40.61%	1,363	10.08%
1976	5,429	45.79%	6,226	52.51%	202	1.70%
1972	6,583	57.09%	4,643	40.27%	305	2.65%
1968	5,791	52.35%	4,618	41.75%	653	5.90%
1964	3,903	32.96%	7,911	66.80%	28	0.24%
1960	7,444	61.99%	4,547	37.87%	17	0.14%
1956	6,830	56.13%	5,316	43.69%	22	0.18%
1952	7,165	57.25%	5,196	41.51%	155	1.24%
1948	4,312	39.67%	6,300	57.96%	258	2.37%
1944	4,874	42.99%	6,365	56.14%	99	0.87%
1940	5,763	45.19%	6,915	54.22%	75	0.59%
1936	4,975	41.51%	6,745	56.27%	266	2.22%
1932	3,695	33.49%	7,067	64.05%	272	2.47%
1928	6,225	59.36%	4,113	39.22%	149	1.42%
1924	5,058	47.65%	2,383	22.45%	3,174	29.90%
1920	5,435	56.62%	3,861	40.22%	303	3.16%
1916	2,459	42.90%	3,094	53.98%	179	3.12%
1912	1,191	22.66%	2,276	43.31%	1,788	34.02%
1908	2,625	46.12%	2,739	48.12%	328	5.76%
1904	2,988	53.05%	2,202	39.10%	442	7.85%
1900	2,950	48.53%	2,950	48.53%	179	2.94%
1896	2,741	46.05%	3,119	52.40%	92	1.55%
1892	2,319	43.70%	2,540	47.86%	448	8.44%
1888	2,374	47.30%	2,322	46.26%	323	6.44%
1884	2,356	47.27%	2,593	52.03%	35	0.70%
1880	2,452	47.46%	1,520	29.42%	1,194	23.11%

• National Register of Historic Places listings in Marion County, Iowa

• Official Marion County, Iowa Website

41°19′52″N 93°06′08″W / 41.33111°N 93.10222°W / 41.33111; -93.10222