Deer Grove, Illinois. Deer Grove is a village in Whiteside County, Illinois, United States. The population was given as 45 in the 2010 census, down from 48 in 2000. Deer Grove is located at 41°36′28″N 89°41′30″W / 41.60778°N 89.69167°W / 41.60778; -89.69167 (41.607822, -89.691534).