| Rex River | |
| Map Size: | 300 |
| Pushpin Map: | Washington#USA |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of the mouth of the Rex River in Washington |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Washington |
| Subdivision Type4: | County |
| Subdivision Name4: | King |
| Discharge1 Location: | river mile 3.0[1] |
| Discharge1 Min: | 3cuft/s |
| Discharge1 Avg: | 100cuft/s[2] |
| Discharge1 Max: | 4200cuft/s |
| Source1: | Cascade Range |
| Source1 Coordinates: | 47.3019°N -121.6025°W |
| Mouth: | Cedar River |
| Mouth Location: | Chester Morse Lake |
| Mouth Coordinates: | 47.3786°N -121.6967°W |
| Basin Size: | 13.4sqmi |
The Rex River is a river in the U.S. state of Washington. It originates near the crest of the Cascade Mountains and flows northwest to join the Cedar River in the Chester Morse Lake reservoir. The Cedar River flows to Lake Washington and, ultimately, Puget Sound. Tributaries of the Rex River include Pine Creek, Lindsay Creek, and Boulder Creek.
The Rex River is entirely contained within the Cedar River Municipal Watershed, an area managed by the City of Seattle which provides two-thirds of the water supply for the greater Seattle metropolitan region.[3] [4]