| William Dietz | |
| Office: | New York State Senate (3rd D.) |
| Term Start: | 1830 |
| Term End: | 1833 |
| State2: | New York |
| District2: | 12th |
| Term Start2: | March 4, 1825 |
| Term End2: | March 3, 1827 |
| Preceded2: | Lewis Eaton |
| Succeeded2: | John I. De Graff |
| Office3: | New York State Assembly (Schoharie Co.) |
| Term Start3: | 1814 |
| Term End3: | 1815 |
| Term4: | 1823 |
| Birth Date: | 28 June 1778 |
| Birth Place: | Schoharie, New York |
| Death Place: | Schoharie, New York |
| Resting Place: | St. Paul’s Lutheran Cemetery |
| Party: | Jacksonian |
| Branch: | New York militia |
| Rank: | Colonel |
William Dietz (June 28, 1778 – August 24, 1848) was an American farmer and politician from New York. From 1825 to 1827, he served one term in the U.S. House of Representatives.
He attended the district schools and engaged in agricultural pursuits. He was Town Clerk of Schoharie and Supervisor of Schoharie County.
He was a colonel of the State Militia.
He was a member of the New York State Assembly (Schoharie Co.) in 1814, 1814–15 and 1823.
Dietz was elected as a Jacksonian to the 19th United States Congress, holding office from March 4, 1825, to March 3, 1827.
He was a member of the New York State Senate (3rd D.) from 1830 to 1833, sitting in the 53rd, 54th, 55th and 56th New York State Legislatures.
He was a presidential elector in 1832, voting for Andrew Jackson and Martin Van Buren.
He was County Superintendent of the Poor from 1834 to 1835.
He died on August 24, 1828, and was buried at the St. Paul's Lutheran Cemetery in Schoharie.