Clay County is located in the U.S. state of Missouri and is part of the Kansas City metropolitan area. As of the 2010 census, the county had a population of 221,939, making it the fifth-most populous county in Missouri. Its county seat is Liberty. The county was organized January 2, 1822, and named in honor of U.S. Representative Henry Clay from Kentucky, later member of the United States Senate and United States Secretary of State.
According to the U.S. Census Bureau, the county has a total area of 409 square miles (1,060 km), of which 397 square miles (1,030 km) is land and 11 square miles (28 km) (2.8%) is covered by water. It is the fourth-smallest county in Missouri by area.
As of the census of 2010, 221,939 people, 72,558 households, and 50,137 families resided in the county. The population density was 558 people per square mile (216/km²). The 93,918 housing units averaged 236 per square mile (91/km). The racial makeup of the county was 87.46% White, 5.18% Black or African American, 0.53% Native American, 2.05% Asian, 0.26% Pacific Islander, 1.77% from other races, and 2.75% from two or more races. About 5.90% of the population were Hispanic or Latino of any race. As of the census of 2000, 23.3% were of German, 14.5% American, 11.0% English, 10.8% Irish, and 5.6% Italian ancestry.
Of the 72,558 households, 33.80% had children under the age of 18 living with them, 55.40% were married couples living together, 10.20% had a female householder with no husband present, and 30.90% were not families. About 25.20% of all households were made up of individuals, and 7.40% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.00.
In the county, the population was distributed as 25.80% under the age of 18, 8.70% from 18 to 24, 32.30% from 25 to 44, 22.30% from 45 to 64, and 10.80% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 94.60 males. For every 100 females age 18 and over, there were 91.80 males.
In 2015 the median income for a household in Clay County was $62,099. The income per capita in Clay county was $29,793.
In 2010 the median income for a household in the county was $48,347, and for a family was $56,772. Males had a median income of $40,148 versus $27,681 for females. The per capita income for the county was $23,144. About 3.80% of families and 5.50% of the population were below the poverty line, including 6.40% of those under age 18 and 5.50% of those age 65 or over.
Registered voters number 151,042.