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

At this time, 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 3 meant their term ended with this Congress, requiring reelection in 1908; Class 1 meant their term began in the last Congress, requiring reelection in 1910; and Class 2 meant their term began in this Congress, requiring reelection in 1912.

The names of members of the House of Representatives elected statewide on the general ticket or otherwise at-large, are preceded by an "At-large," and the names of those elected from districts, whether plural or single member, are preceded by their district numbers.

The directory after the pages of terms of service lists committees of the Senate, House (Standing with Subcommittees, Select and Special) and Joint and, after that, House/Senate committee assignments.