Thompson River (Missouri)

The Thompson River is the largest tributary of the Grand River in the central United States, flowing from southern Iowa into Missouri. In Iowa, it is known simply as the Grand River and passes near the city of Grand River. The river is 188 mi long, and its drainage basin is roughly 1850 mi2, of which 1111 mi2 are in Missouri.

It rises in the agricultural lands of Adair County, Iowa, a few miles northeast of Greenfield. The river initially flows east then bends south, passing Macksburg and Davis City and crossing Interstate 35. It then flows into Missouri, where much of its course is channelized. The Weldon River joins at the town of Trenton, the largest settlement along the Thompson River. Below Trenton, the Thompson meanders south for another 25 mi, joining the Grand River just north of Utica in Livingston County.