The Black River is a river in Thurston County in the U.S. state of Washington. It is approximately 25 miles (40 km) long with a drainage basin of about 144 square miles (370 km).

The fur trader John Work was the first to describe the Black River in 1824: "The Black River so named from the colour of its water ... A great many dead salmon are in the river, and many that are just alive and barely able to move through the water."

The Black River's source is Black Lake, located about 3 miles (4.8 km) west of Tumwater. The river flows generally south, through Littlerock, near the Mima Mounds Natural Area Preserve, then southwest, passing through the Black River Habitat Management Area and the town of Rochester, before meandering west through the community of Gate and entering Grays Harbor County, where it empties into the Chehalis River in the Chehalis Indian Reservation.

The Black River Unit of the Nisqually National Wildlife Refuge extends about 5 miles (8 km) along the river immediately south of Black Lake.

• List of rivers in Washington

• U.S. Geological Survey Geographic Names Information System: Black River