High Quality Content by WIKIPEDIA articles! Mission Hills is a city in Johnson County, Kansas, United States. As of the 2010 census, the city population was 3,498. The city is a suburb of Kansas City, Missouri, which is adjacent to the east, across the aptly named State Line Road. Mission Hills was originally developed by noted Kansas City developer J. C. Nichols beginning in the 1920s as part of his Country Club District plan.