Plain City is a city in Weber County, Utah, United States. The population was 5,476 at the 2010 census. It is part of the Ogden–Clearfield, Utah Metropolitan Statistical Area.
According to the United States Census Bureau, the city has a total area of 11.73 square miles and 0.23 square miles of water.
As of the census of 2000, there were 3,489 people, 979 households, and 868 families residing in the city. The population density was 935.3 people per square mile (361.2/km²). There were 1,001 housing units at an average density of 268.3 per square mile (103.6/km²). The racial makeup of the city was 97.39% White, 0.03% African American, 0.32% Native American, 0.49% Asian, 0.03% Pacific Islander, 0.63% from other races, and 1.12% from two or more races. Hispanic or Latino of any race were 2.03% of the population.
There were 979 households out of which 52.9% had children under the age of 18 living with them, 80.3% were married couples living together, 6.3% had a female householder with no husband present, and 11.3% were non-families. 10.1% of all households were made up of individuals and 4.5% had someone living alone who was 65 years of age or older. The average household size was 3.56 and the average family size was 3.84.
In the city, the population was spread out with 36.4% under the age of 18, 11.6% from 18 to 24, 26.9% from 25 to 44, 18.8% from 45 to 64, and 6.4% who were 65 years of age or older. The median age was 27 years. For every 100 females, there were 103.0 males. For every 100 females age 18 and over, there were 99.1 males.
The median income for a household in the city was $57,601, and the median income for a family was $60,000. Males had a median income of $41,477 versus $26,532 for females. The per capita income for the city was $17,688. About 1.3% of families and 2.0% of the population were below the poverty line, including 2.4% of those under age 18 and none of those age 65 or over.