De Soto is a city in Johnson and Leavenworth counties in the U.S. state of Kansas, and part of the Kansas City Metropolitan Area. The vast majority of the city, 11.13 sq. mi., lies within Johnson County. As of the 2010 census, the city population was 5,720, and the 2015 census estimate is 6,074. The area code is 913, and the two zip codes are 66018 and 66019.