William Dietz (June 28, 1778 – August 24, 1848) was an American farmer and politician from New York.

He attended the district schools and engaged in agricultural pursuits.

He was a member of the New York State Assembly (Schoharie Co.) in 1814, 1814–15 and 1823.

He was a presidential elector in 1832, voting for Andrew Jackson and Martin Van Buren.

He died on August 24, 1828, and was buried at the St. Paul's Lutheran Cemetery in Schoharie.