Washington Creek rises on the west flank of Sonoma Mountain and descends to the southwest.

It crosses under Adobe Road just north of East Washington Street, then parallels East Washington Street through Rooster Run Golf Club and into suburban Petaluma, crossing under Sonoma Mountain Parkway and Maria Drive.

Emerging from the U.S. 101 interchange, the creek flows westward, crossing under Madison Street and Holly Lane to enter the Petaluma River just north of the Payran Street bridge.

On March 7, 2000, a Sonoma Mountain dairy rancher pleaded "no contest" to charges that in 1999 he dumped 732,000 US gal (2,770 m3) of manure and urine into Washington Creek.

This was reportedly the first time a Sonoma County dairy farmer had faced fines stemming from criminal charges in a creek pollution case.