On August 2, 1886, Adelaide Post Office opens. George W. Cunningham is the first postmaster. Adelaide is located 19 miles south of Seattle along Puget Sound, about three miles from Dash Point.
Adelaide was a place of orchards and farms: The main products were fruits and vegetables. In 1889, 25 school aged children lived in the district. Adelaide had a sawmill named Martin & Co. It was on the Seattle, Lakeshore & Eastern railroad line, and there was a steamer to Tacoma.
The post office closed permanently on January 15, 1931.