Plymouth County is the westernmost county in the U.S. state of Iowa. As of the 2020 census, the population was 25,698, and was estimated to be 25,697 in 2025. Plymouth County was named after Plymouth, Massachusetts.
Plymouth County is part of the Sioux City metropolitan area.
History
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 United States Census Bureau, the county has a total area of , of which is land and (0.10%) is water. It is the fourth-largest county in Iowa by total area.
Adjacent counties
- Sioux County (north)
- Cherokee County (east)
- Woodbury County (south)
- Union County, South Dakota (west)
Transportation
Major highways
- x20px U.S. Highway 75
- x20px Iowa Highway 3
- x20px Iowa Highway 12
- x20px Iowa Highway 60
- x20px Iowa Highway 140
Airport
Le Mars Municipal Airport is located in Plymouth County, two nautical miles (3.7 km) southwest of the central business district of Le Mars.