It crosses into northern Illinois and joins the Pecatonica River in northern Winnebago County, approximately 5 mi (8 km) south of the state line and approximately 15 mi (25 km) NNE of Rockford.
It crosses into northern Illinois and receives the Pecatonica River in northern Winnebago County, approximately 5 mi (8 km) south of the state line. It flows east and joins the Rock at Rockton, approximately 15 mi (25 km) north of Rockford.