Plainfield is a city in Bremer County, Iowa, United States. The population was 393 at the 2020 census, a decrease of 45, or 10.3%, from 438 in 2000. It is part of the Waterloo–Cedar Falls Metropolitan Statistical Area. Geography Plainfield is located at (42.844652, -92.534623). According to the United States Census Bureau, the city has a total area of , all land. Demographics 2010 census As of the census of 2010, there were 436 people, 185 households, and 123 families residing in the city. The population density was . There were 197 housing units at an average density of . The racial makeup of the city was 97.9% White, 0.5% African American, 0.2% Pacific Islander, 0.2% from other races, and 1.1% from two or more races. Hispanic or Latino of any race were 0.5% of the population. There were 185 households, of which 30.3% had children under the age of 18 living with them, 55.7% were married couples living together, 8.1% had a female householder with no husband present, 2.7% had a male householder with no wife present, and 33.5% were non-families. 28.1% of all households were made up of individuals, and 11.8% had someone living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.90. The median age in the city was 37.8 years. 27.1% of residents were under the age of 18; 7.4% were between the ages of 18 and 24; 24.3% were from 25 to 44; 25.9% were from 45 to 64; and 15.4% were 65 years of age or older. The gender makeup of the city was 50.2% male and 49.8% female. 2000 census As of the census of 2000, there were 438 people, 194 households, and 123 families residing in the city. The population density was . There were 202 housing units at an average density of . The racial makeup of the city was 99.54% White, 0.23% Native American, and 0.23% from two or more races. Hispanic or Latino of any race were 0.91% of the population. There were 194 households, out of which 29.4% had children under the age of 18 living with them, 56.2% were married couples living together, 7.2% had a female householder with no husband present, and 36.1% were non-families. 30.9% of all households were made up of individuals, and 16.5% had someone living alone who was 65