Plymouth County
Also known as Plymouth County, Iowa, Plymouth County, IA
county in Iowa, United States
Key facts
- Country
- United States
- State
- Iowa
- Founded
- January 15, 1851 (created), October 27, 1858 (organized)
- Named after
- Plymouth, Massachusetts
- Seat
- Le Mars
- Largest city
- Le Mars
- Total
- 863.668 sq mi (2,236.89 km )
- Land
- 862.828 sq mi (2,234.71 km )
- Water
- 0.840 sq mi (2.18 km ) 0.10%
- Estimate 2025
- 25,697
- Density
- 29.783/sq mi (11.499/km )
- Time zone
- UTC−6 ( Central )
- Summer dst
Article
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. The county seat and the largest city is Le Mars. Plymouth County was named after Plymouth, Massachusetts.
Plymouth County is part of the Sioux City metropolitan area.