Johnston is located in Polk county Iowa with a geographic area of 19.4 square miles. The total population in Johnston is 22,077 with 47.9% male and 52.1% female. Children under age 5 represent 6.6% of the population, under age 18 equal 27.5% of the population and over age 65 is 15.3% of the population. The median household income is $92,984, per capita income is $49,775. There are a total of 8,925 housing units with 73.1% owner occupied. Education includes 16.5% of residents that are high school graduates and 58.2% with a bachelor's degree or higher. The average temperature in Johnston in the summer is 72 degrees, and in the winter 23 degrees.
