Lake st. louis is located in St. charles county Missouri with a geographic area of 8.5 square miles. The total population in Lake st. louis is 16,357 with 49.9% male and 50.1% female. Children under age 5 represent 3.3% of the population, under age 18 equal 19.7% of the population and over age 65 is 20.9% of the population. The median household income is $100,122, per capita income is $46,974. There are a total of 6,557 housing units with 81.4% owner occupied. Education includes 12.1% of residents that are high school graduates and 53.3% with a bachelor's degree or higher. The average temperature in Lake st. louis in the summer is 77 degrees, and in the winter 32 degrees.