Apportionment Act of 1911

The Apportionment Act of 1911 was an apportionment bill passed by the United States Congress on August 8, 1911. The law initially set the number of members of the United States House of Representatives at 433, effective with the 63rd Congress on March 4, 1913. It also included, in section 2, a provision to add an additional seat for each of the anticipated new states of Arizona and New Mexico, bringing the total number of seats to 435.

Previous apportionment

To give effect to the requirements of Article One, Section 2, Clause 3 of the United States Constitution and Section Two of the Fourteenth Amendment that United States representatives be apportioned to the states in proportion to their respective populations, Congress would pass Apportionment Acts following each Census, starting with the Apportionment Act of 1792.
Prior to the Apportionment Act of 1911, the Hamilton/Vinton method was used in the apportionment of seats since 1850. In addition to setting the number of U.S. Representatives at 435, the Apportionment Act of 1911 returned to the Webster method of apportionment of U.S. Representatives.

Subsequent apportionment

For the first and only time, Congress failed to pass an apportionment act after the 1920 census. This left the allocations of the Act of 1911 in place until the 1930 census. The Reapportionment Act of 1929 established a method for reallocating seats among the states, given population shifts and the maximum of 435 representatives. A 1941 amendment to the 1929 act made the apportionment process self-executing after each decennial census. This lifted Congress's responsibility to pass an apportionment act for each census, and ensured that the events surrounding the 1920 census would not happen again. The number of U.S. Representatives increased temporarily to 437 when Alaska and Hawaii were admitted as states in 1959 during the 86th Congress. After the 1960 United States census and the 1962 election, the standard reapportionment brought the number back to 435.