William J. Cornwell (August 24, 1809 in Stanford, Dutchess County, New York – 1896) was an American lawyer and politician from New York.
He married Marietta Sheldon, and they had three children.
He practiced law in Weedsport, New York.
He was a member of the New York State Assembly (Cayuga Co.) in 1846 and 1847.
He was a member of the New York State Senate (24th D.) in 1848 and 1849.