William David Thomas was an American pharmacist and politician from Hoosick Falls, New York. A Republican, he was most notable for his service as a member of the United States House of Representatives from New York, a position he held from 1934 until his death.

New York's 29th congressional district is an obsolete congressional district for the United States House of Representatives which most recently included a portion of the Appalachian mountains in New York known as the "Southern Tier." It was most recently represented by Tom Reed. This district number became obsolete for the 113th Congress in 2013 as a result of the 2010 census. Most of the former 29th district remained intact and was to be renumbered as the 23rd district.