Lyon County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 25,269. Its county seat is Marshall.

Lyon County comprises the Marshall, MN Micropolitan Statistical Area.

The county was established by two acts of the Minnesota state legislature, dated March 6, 1868, and March 2, 1869. The county seat was designated as Marshall. The county was named for Nathaniel Lyon, an Army officer who served in the Dakota and Minnesota territories before being killed in the Civil War in 1861. He had achieved the rank of general by his death. The county was much larger until an act passed on March 6, 1873, made the western 43% the new Lincoln County.

The Yellow Medicine River flows northeast through the upper portion of the county, the Redwood River flows northeast through the central part, and the Cottonwood River flows northeast through the lower part. The county's terrain consists of low rolling hills, etched by drainages and gullies. It slopes to the north and east, with its highest point near its southwest corner, at 1,729 ft (527 m) ASL. The county has a total area of 722 square miles (1,870 km), of which 715 square miles (1,850 km) is land and 7.1 square miles (18 km) (1.0%) is water.

• Southwest Minnesota Regional Airport (MML)
• Tracy Municipal Airport (TKC)

Historical population

Census	Pop.	Note	%±
1880	6,257		—
1890	9,501		51.8%
1900	14,591		53.6%
1910	15,722		7.8%
1920	18,837		19.8%
1930	19,328		2.6%
1940	21,569		11.6%
1950	22,253		3.2%
1960	22,655		1.8%
1970	24,273		7.1%
1980	25,207		3.8%
1990	24,789		−1.7%
2000	25,425		2.6%
2010	25,857		1.7%
2020	25,269		−2.3%
2023 (est.)	25,427		0.6%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2020

Lyon County Racial Composition

Race	Num.	Perc.
White (NH)	20,535	81.26%
Black or African American (NH)	906	3.6%
Native American (NH)	84	0.3%
Asian (NH)	1,263	5%
Pacific Islander (NH)	3	0.01%
Other/Mixed (NH)	734	2.9%
Hispanic or Latino	1,744	7%

As of the 2000 census, there were 25,425 people, 9,715 households, and 6,334 families in the county. The population density was 35.6 per square mile (13.7/km). There were 10,298 housing units at an average density of 14.4 per square mile (5.6/km). The racial makeup of the county was 93.58% White, 1.49% Black or African American, 0.31% Native American, 1.67% Asian, 0.02% Pacific Islander, 1.89% from other races, and 1.04% from two or more races. 3.97% of the population were Hispanic or Latino of any race. 33.9% were of German, 15.5% Norwegian and 10.5% Belgian ancestry.

There were 9,715 households, out of which 33.00% had children under the age of 18 living with them, 55.10% were married couples living together, 7.10% had a female householder with no husband present, and 34.80% were non-families. 27.90% of all households were made up of individuals, and 12.40% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 3.09.

The county population contained 26.20% under the age of 18, 13.30% from 18 to 24, 26.50% from 25 to 44, 19.50% from 45 to 64, and 14.60% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 95.70 males. For every 100 females age 18 and over, there were 93.20 males.

The median income for a household in the county was $38,996, and the median income for a family was $48,512. Males had a median income of $32,102 versus $21,445 for females. The per capita income for the county was $18,013. About 6.30% of families and 10.10% of the population were below the poverty line, including 10.00% of those under age 18 and 12.70% of those age 65 or over.

Lyon County has been a traditional Republican stronghold. In only one national election since 1980 has the county selected the Democratic Party candidate (as of 2024).

United States presidential election results for Lyon County, Minnesota

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	8,400	64.67%	4,284	32.98%	306	2.36%
2020	7,979	61.89%	4,634	35.94%	280	2.17%
2016	7,256	59.40%	3,825	31.31%	1,134	9.28%
2012	6,594	53.23%	5,465	44.12%	329	2.66%
2008	6,315	49.69%	6,110	48.08%	283	2.23%
2004	7,203	56.84%	5,292	41.76%	178	1.40%
2000	6,087	52.98%	4,737	41.23%	665	5.79%
1996	4,932	42.97%	5,062	44.11%	1,483	12.92%
1992	4,591	37.25%	4,481	36.36%	3,252	26.39%
1988	5,969	50.86%	5,657	48.20%	110	0.94%
1984	7,170	56.64%	5,389	42.57%	100	0.79%
1980	5,852	45.33%	5,626	43.58%	1,433	11.10%
1976	5,036	40.42%	7,122	57.17%	300	2.41%
1972	5,820	50.04%	5,614	48.27%	196	1.69%
1968	4,331	43.46%	5,317	53.35%	318	3.19%
1964	3,165	32.22%	6,649	67.69%	8	0.08%
1960	4,740	46.00%	5,550	53.86%	15	0.15%
1956	5,188	55.27%	4,190	44.64%	8	0.09%
1952	6,015	59.74%	4,030	40.02%	24	0.24%
1948	3,054	32.89%	6,144	66.16%	88	0.95%
1944	3,617	43.60%	4,640	55.94%	38	0.46%
1940	4,305	44.96%	5,234	54.66%	36	0.38%
1936	2,551	30.28%	5,163	61.29%	710	8.43%
1932	2,264	30.67%	4,989	67.57%	130	1.76%
1928	4,058	54.93%	3,274	44.32%	56	0.76%
1924	3,519	53.70%	334	5.10%	2,700	41.20%
1920	4,557	73.16%	1,232	19.78%	440	7.06%
1916	1,389	38.97%	1,893	53.11%	282	7.91%
1912	460	15.65%	1,068	36.34%	1,411	48.01%
1908	1,618	56.69%	1,043	36.55%	193	6.76%
1904	2,394	81.82%	330	11.28%	202	6.90%
1900	1,844	64.61%	879	30.80%	131	4.59%
1896	1,623	52.83%	1,351	43.98%	98	3.19%
1892	1,068	50.88%	486	23.15%	545	25.96%

• National Register of Historic Places listings in Lyon County, Minnesota

• Lyon County government website

44°25′N 95°50′W / 44.41°N 95.84°W / 44.41; -95.84