Flint Hill is a city in St. Charles County, Missouri, United States. The population was 379 at the 2000 census.
According to the United States Census Bureau, the city has a total area of 2.5 square miles (6.4 km²), all of it land.
As of the census of 2000, there were 379 people, 136 households, and 107 families residing in the city. The population density was 152.2 people per square mile (58.8/km²). There were 138 housing units at an average density of 55.4/sq mi (21.4/km²). The racial makeup of the city was 97.10% White, 0.53% African American, 0.26% Asian, and 2.11% from two or more races. Hispanic or Latino of any race were 0.53% of the population.
There were 136 households out of which 40.4% had children under the age of 18 living with them, 72.1% were married couples living together, 3.7% had a female householder with no husband present, and 21.3% were non-families. 19.9% of all households were made up of individuals and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.79 and the average family size was 3.22.
In the city the population was spread out with 28.2% under the age of 18, 7.4% from 18 to 24, 31.1% from 25 to 44, 22.7% from 45 to 64, and 10.6% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 106.0 males. For every 100 females age 18 and over, there were 109.2 males.
The median income for a household in the city was $47,500, and the median income for a family was $62,750. Males had a median income of $43,333 versus $25,000 for females. The per capita income for the city was $21,194. About 2.9% of families and 2.2% of the population were below the poverty line, including none of those under age 18 and 13.5% of those age 65 or over.