According to the U.S. Census Bureau, the county has a total area of 427 square miles (1,110 km2), of which 420 square miles (1,100 km2) is land and 6.6 square miles (17 km2) (1.5%) is water. The county's southwestern border with Kansas is formed by the Missouri River.
There were 29,278 households out of which 34.10% had children under the age of 18 living with them, 57.00% were married couples living together, 8.80% had a female householder with no husband present, and 30.90% were non-families. 24.90% of all households were made up of individuals and 6.00% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 3.00.
In the county the population was spread out with 25.80% under the age of 18, 8.30% from 18 to 24, 32.60% from 25 to 44, 24.50% from 45 to 64, and 8.80% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 98.10 males. For every 100 females age 18 and over, there were 95.50 males.
The median income for a household in the county was $55,849, and the median income for a family was $65,236. Males had a median income of $44,310 versus $31,005 for females. The per capita income for the county was $26,356. About 3.30% of families and 4.80% of the population were below the poverty line, including 5.70% of those under age 18 and 5.70% of those age 65 or over.
The Republican Party controls politics at the local level in Platte County. Republicans hold all of the elected positions in the county. However, GovernorJay Nixon carried the county in his two successful elections, and in 2004, Claire McCaskill of Jackson County narrowly won a majority of the county's votes over Republican victor Matt Blunt.
District 30 – Nick Marshall (R-Parkville). Consists of the communities of Camden Point, Dearborn, Edgerton, Farley, Ferrelview, Platte City, Ridgely, Tracy, Weatherby Lake, and a small portion of the city of Kansas City.
Missouri House of Representatives - District 30 – Platte County (2010)