William Adam Piper (May 21, 1826, Pennsylvania – August 5, 1899, San Francisco) was an American politician and a businessperson.

He moved to California in 1848 and settled in San Francisco in 1849, where he engaged in mercantile pursuits.

William Adam Piper was elected as a Democrat to the 44th United States Congress.

He received only 49.06% of the vote, the opposition being divided between Iva P. Rankin running as a Republican and the independent candidate John F.

He continued his business activities, and he died on August 5, 1899, in San Francisco, California.