Mill Plain is an unincorporated area in Clark County, Washington, United States. At the 2000 census it was defined as a census-designated place (CDP) and had a population of 7,400. The Place was not listed as a CDP for the 2010 census.

The Mill Plain Place is located in southern Clark County at 45°38′41″N 122°29′34″W / 45.64472°N 122.49278°W / 45.64472; -122.49278 (45.644728, -122.492878). It is bordered by the city of Vancouver to the west and south and by the city of Camas to the southeast.

According to the United States Census Bureau, in 2000 the CDP had a total Place of 6.0 square miles (15.5 km²), all of it land.

As of the census of 2000, there were 7,400 people, 2,379 households, and 1,953 families residing in the CDP. The population density was 1,236.9 people per square mile (477.8/km²). There were 2,500 housing units at an average density of 417.9/sq mi (161.4/km²). The racial makeup of the CDP was 87.34% White, 1.62% African American, 0.57% Native American, 6.23% Asian, 0.11% Pacific Islander, 0.59% from additional races, and 3.54% from two or more races. Hispanic or Latino of any race were 2.66% of the population.

There were 2,379 households, out of which 49.7% had children under the age of 18 living bearing in mind them, 71.0% were married couples animate together, 7.7% had a female householder behind no husband present, and 17.9% were non-families. 12.6% of whatever households were made in the works of individuals, and 3.5% had someone lively alone who was 65 years of age or older. The average household size was 3.11 and the average family size was 3.41.