The 91st United States Congress began on January 3, 1969. There were 12 new senators (four Democrats, eight Republicans) and 38 new representatives (19 Democrats, 19 Republicans), as well as one new delegate (a Democrat), at the start of the first session. Additionally, four senators (two Democrats, two Republicans) and 14 representatives (seven Democrats, seven Republicans) took office on various dates in order to fill vacancies during the 91st Congress before it ended on January 3, 1971.
Due to redistricting in multiple states, eight representatives were elected from newly created seats.