Green River (Illinois) Green River (Illinois) The Green River is an tributary of the Rock River in northwestern Illinois in the United States. Via the Rock, it is part of the Mississippi River watershed. Much of the Green's course has been straightened and channelized. The Green rises in northern Lee County and flows initially southwestward through Lee, Whiteside and Bureau Counties, passing the town of Amboy. It turns westward in Bureau County and flows into Henry County, where it roughly parallels the Hennepin Canal and passes the towns of Colona and Green Rock. It joins the Rock River just west of Green Rock,
Big Thompson River tributary flows east, through the town of Glen Haven, where it merges with the Big Thompson River in the town of Drake, in the Big Thompson Canyon. From Lake Estes, the river descends 1/2 mile (800 m) in elevation through the mountains in the spectacular 25 mi (40 km) Big Thompson Canyon, emerging from the foothills west of Loveland. It flows eastward, south of Loveland across the plains into Weld County and joins the South Platte approximately 5 mi (8 km) south of Greeley. It receives the Little Thompson River approximately four mi (6 km) upstream from its mouth. Water