Sunnydale, WashingtonSunnydale is an unincorporated community in Thurston County, in the U.S. state of Washington. The community is situated on Old Highway 99 between Grand Mound and Tenino.HistorySunnydale took its name from a nearby poultry farm.Parks and recreationMillersylvania State Park is north of the area, and Sunnydale lies east of the Scatter Creek Wildlife Recreation Area.