Yorkville is a city partially in Kendall and Kane counties, Illinois, United States. The population was 6,189 at the 2000 United States Census and had grown to 16,921 as of the 2010 census. It is the county seat of Kendall County. Yorkville is in the center of Kendall County, the fastest-growing county in Illinois and according to recent statistics released in June 2010, by CNN, is the fastest-growing county in the United States.