The apportionment of seats in the House of Representatives was based on the 1900 United States census.

Additional House seats were assigned to the two new states of New Mexico and Arizona.

At this time, most senators were elected by the state legislatures 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, In this Congress, Class 2 meant their term ended with this Congress, requiring reelection in 1912; Class 3 meant their term began in the last Congress, requiring reelection in 1914; and Class 1 meant their term began in this Congress, requiring reelection in 1916.

The names of members of the House of Representatives are preceded by their district numbers.