Clayton is the county seat of St. Louis County, part of the Greater St. Louis metropolitan area. The population was 12,825 at the 2000 census. The city was organized in 1877 and is named after Ralph Clayton, who donated the land for the courthouse. Clayton has a highly rated public school system,  possibly connected to its comparatively high real estate values. Clayton is home to Washington University, Fontbonne University, and Concordia Seminary of the Lutheran Church - Missouri Synod.
Clayton is located at(38.645318, -90.331844).
According to the United States Census Bureau, the city has a total area of 2.5 mi², all land.
As of the census of 2000, there were 12,825 people, 5,370 households, and 2,797 families residing in the city. The population density was 5,164.4/mi². There were 5,852 housing units at an average density of 2,356.5/mi². The racial makeup of the city was 84.94% White, 7.77% African American, 0.12% Native American, 5.62% Asian, 0.03% Pacific Islander, 0.29% from other races, and 1.22% from two or more races. Hispanic or Latino of any race were 1.49% of the population.
There were 5,370 households out of which 25.9% had children under the age of 18 living with them, 43.4% were married couples living together, 6.7% had a female householder with no husband present, and 47.9% were non-families. 40.4% 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 2.09 and the average family size was 2.90.
In the city the population was spread out with 20.1% under the age of 18, 10.7% from 18 to 24, 32.3% from 25 to 44, 22.6% from 45 to 64, and 14.3% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 100.5 males. For every 100 females age 18 and over, there were 98.0 males.
The median income for a household in the city was $64,184, and the median income for a family was $107,346. Males had a median income of $64,737 versus $42,757 for females. The per capita income for the city was $48,055. About 5.0% of families and 7.7% of the population were below the poverty line, including 9.5% of those under age 18 and 3.2% of those age 65 or over.
<googlemap lat="38.643004" lon="-90.33503" width="700" controls="large">38.643004, -90.33503, Clayton, MO, USA</googlemap>