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.
Geography
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' ASL. The county has a total area of, of which is land and is water.
As of the 2000 United States Census, there were 25,425 people, 9,715 households, and 6,334 families in the county. The population density was 35.6/sqmi. There were 10,298 housing units at an average density of 14.4/sqmi. 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.
