| Thompson River | |
| Name Other: | Thompson Fork Grand River |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Iowa, Missouri |
| Length: | 188miles |
| Discharge1 Location: | Trenton, 25.2miles from the mouth[1] |
| Discharge1 Min: | 1cuft/s |
| Discharge1 Avg: | 1059cuft/s[2] |
| Discharge1 Max: | 95000cuft/s |
| Source1: | Near Greenfield |
| Source1 Location: | Adair County, Iowa |
| Source1 Coordinates: | 41.3567°N -94.4311°W[3] |
| Source1 Elevation: | 1360feet |
| Mouth: | Grand River |
| Mouth Location: | Livingston County, Missouri |
| Mouth Coordinates: | 39.7639°N -93.6144°W |
| Mouth Elevation: | 679feet |
| Basin Size: | 1850sqmi |
| Tributaries Left: | Weldon River, Honey Creek |
| Tributaries Right: | Sugar Creek, Hickory Creek |
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.[4] The river is long,[5] and its drainage basin is roughly 1850mi2, of which 1111mi2 are in Missouri.[6]
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 25miles, joining the Grand River just north of Utica in Livingston County.[7]