Stillman Valley is a village in Marion Township, Ogle County, Illinois, United States. It lies east of Byron, south of Rockford and west of Davis Junction. The population was 1,120 at the 2010 census, up from 1,048 in 2000. Stillman Valley Currently has a population of around 3,018. The village is located on the Iowa, Chicago and Eastern Railroad, on the old Chicago Great Western Railway before it merged and was pulled up. Also, Illinois Route 72 runs through the village.