Plainfield is a city in Bremer County, Iowa, United States. The population was 438 at the 2000 census. It is part of the Waterloo–Cedar Falls Metropolitan Statistical Area.
Plainfield is located at 42°50′41″N 92°32′5″W / 42.84472°N 92.53472°W / 42.84472; -92.53472 (42.844652, -92.534623).
According to the United States Census Bureau, the city has a total area of 0.3 square miles (0.9 km²), all of it land.