| Knox River | |
| Pushpin Map: | New Hampshire#USA |
| Pushpin Map Size: | 250 px |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | New Hampshire |
| Subdivision Type3: | County |
| Subdivision Name3: | Grafton |
| Subdivision Type4: | Towns |
| Subdivision Name4: | Enfield |
| Length: | 2.5miles |
| Source1: | George Pond |
| Source1 Location: | Fish Market (Enfield) |
| Source1 Coordinates: | 43.5808°N -72.1014°W |
| Source1 Elevation: | 297order=flipNaNorder=flip |
| Mouth: | Mascoma Lake |
| Mouth Location: | Enfield |
| Mouth Coordinates: | 43.6064°N -72.125°W |
| Mouth Elevation: | 228order=flipNaNorder=flip |
The Knox River is a 2.5adj=midNaNadj=mid[1] river in western New Hampshire in the United States. The river is an inlet of Mascoma Lake, which drains by the Mascoma River to the Connecticut River and ultimately Long Island Sound.
The Knox River lies entirely in the town of Enfield. It begins at the village of Fish Market as the outlet of George Pond and flows northwest through Enfield Center to the southeastern end of Mascoma Lake. The river is paralleled for its entire length by New Hampshire Route 4A.