Plymouth County was formed on January 15, 1851. Settlement began in the county in 1856. In October 1859, the first courthouse was built in Melbourne, formerly located in the southeast quarter of section 34, Plymouth Township, about five to six miles due south of Merrill. The first public school opened its doors there with 32 pupils. In 1872 the county seat was moved to Le Mars and a courthouse and jail were built there in 1873. The present Plymouth County courthouse was built in 1900 of red sandstone. During the Great Depression, farmers in the county organized the Farmers Holiday Group, to keep farm products off the market until the desired price was met. A radical group among them abducted Judge Bradley from his court chamber and threatened to hang him in the front of the courthouse. Bradley was freed, but the governor ordered the national guard to Plymouth County and declared a state of emergency, which effectively ended the group.
Geography
According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is the fourth-largest county by area in Iowa.
The 2010 census recorded a population of 24,986 in the county, with a population density of. There were 10,550 housing units, of which 9,875 were occupied.
2000 census
As of the census of 2000, there were 24,849 people, 9,372 households, and 6,804 families in the county. The population density was 29 people per square mile. There were 9,880 housing units at an average density of 11 per square mile. The racial makeup of the county was 98.16% White, 0.29% Black or African American, 0.14% Native American, 0.27% Asian, 0.06% Pacific Islander, 0.46% from other races, and 0.62% from two or more races. 1.32% of the population were Hispanic or Latino of any race. Of the 9,372 households 35.70% had children under the age of 18 living with them, 63.30% were married couples living together, 6.20% had a female householder with no husband present, and 27.40% were non-families. 24.00% of households were one person and 12.00% were one person aged 65 or older. The average household size was 2.61 and the average family size was 3.12. The age distribution was 28.30% under the age of 18, 7.20% from 18 to 24, 26.40% from 25 to 44, 22.00% from 45 to 64, and 16.00% 65 or older. The median age was 38 years. For every 100 females there were 98.80 males. For every 100 females age 18 and over, there were 95.70 males. The median household income was $41,638 and the median family income was $50,009. Males had a median income of $33,566 versus $22,558 for females. The per capita income for the county was $19,442. About 4.40% of families and 6.00% of the population were below the poverty line, including 6.70% of those under age 18 and 6.40% of those age 65 or over.
