The Cedar River is a short stream flowing into the north end of Willapa Bay in the U.S. state of Washington.

The Cedar River originates near Seastrand Ridge in the Willapa Hills, about a mile east of the Pacific Ocean near Heather and Grayland Beach State Park, just south of Grayland.

[6] The mouth of the Cedar River merges with Willapa Bay in a tidally-influenced estuary.

There is a 275 acre protected unit called the Cedar River Estuary, managed by Forterra.

This area is a tidal ecosystem with salt marshes, tidelands, and coniferous forests.