The apportionment of seats in the House of Representatives was based on the 1910 United States census.

[1] The count below identifies party affiliations at the beginning of the first session of this Congress, and includes members from vacancies and newly admitted states, when they were first seated.

At the end of the first month of the first session of Congress, Republicans gained control of the Senate through a VP-tie-breaking majority.

They were elected every two years, with one-third beginning new six-year terms with each Congress.

Preceding the names in the list below are Senate class numbers, which indicate the cycle of their election.