William Dietz (28 June 1778-24 August 1848) was a member of the US House of Representatives (D-NY 12) from 4 March 1825 to 3 March 1827, succeeding Lewis Eaton and preceding John I. De Graff. Born in Schoharie, he served as town clerk, as a colonel of the state militia, in the State Assembly from 1814 to 1815 and in 1823, in Congress, and in the state senate from 1830 to 1833.