In Philadelphia, the Framers spent untold hours discussing the basis of representation for the new government and then fell to haggling over the number of Representatives to be elected from each state for the House of Representatives. A majority of delegations set the initial size of the House at a modest sixty-five Members, defeating James Madison’s wish to have it doubled. They wished to leave Congress the flexibility to set numbers in the future, making sure that Congress would not allow for more than one Representative for every 30,000 persons, a last-minute modification of the original floor of 40,000 persons.

At the ratifying conventions, the Anti-Federalists were extremely exercised over the clause. George Mason, for example, inveighed against the small number of Representatives during the debates at the Virginia ratifying convention. James Madison accurately summarized their objections in The Federalist No. 55:

[F]irst, that so small a number of representatives will be an unsafe depositary of the public interests; secondly, that they will not possess a proper knowledge of the local circumstances of their numerous constituents; thirdly, that they will be taken from that class of citizens which will sympathize least with the feelings of the mass of the people, and be most likely to aim at a permanent elevation of the few on the depression of the many; fourthly, that defective as the number will be in the first instance, it will be more disproportionate, by the increase of the people, and the obstacles which will prevent a correspondent increase of the representatives.

Madison spent much time rebutting these objections. “Nothing can be more fallacious than to found our political calculations on arithmetical principles,” he declared. He assured his audience that Congress would increase the number of Representatives as the population grew; that the Senate would not stand in the way; that there was more danger in a cabal of the few forming in a large assembly than in a small one; that there were sufficient checks against corruption within the Constitution; and that Representatives needed knowledge only over subjects they could legislate upon, namely, commerce, taxation, and the militia.

Behind the debate between the Federalists and the Anti-Federalists lay different understandings of the future course of American republicanism. The Anti-Federalists did not believe that the country could grow and still remain republican, a proposition rebutted in Madison’s classic argument in The Federalist No. 10. At the Constitutional Convention, Madison resisted any built-in increase to the numbers of Representatives, arguing that population growth would “render the number of Representatives excessive.” Nathaniel Gorham of Massachusetts responded, “It is not to be supposed that the Gov’t will last so long as to produce this effect. Can it be supposed that this vast Country including the Western territory will 150 years hence remain one nation?”

In response to Anti-Federalist objections, Congress sent twelve amendments to the states for ratification, the first of which changed the method of calculating the number of Representatives. Instead of there being no more than one Representative for 30,000 people, the amendment would have required at least one Representative for 30,000, or later, 40,000 and 50,000 as the population grew. But the amendment failed to achieve ratification, the only one of the original twelve never to have been approved by the states. The Federalist vision of the Union prevailed.

It was not clear whether the Allocation of Representatives Clause required the national average district population to be not less than 30,000, or whether a state’s average district population had to be at least that number. Interestingly, President George Washington vetoed Congress’s first apportionment plan because eight states would have had average district populations of less than 30,000, which he thought in violation of this Clause.

True to Madison’s prediction, Congress nonetheless dutifully increased the number of Representatives as the population grew. By 1833, Justice Joseph Story would write in his Commentaries on the Constitution of the United States that the dire predictions of the Anti-Federalists “have all vanished into air, into thin air.” After the Civil War, Southern representation increased with the ending of slavery and the three-fifths rule. Congress, however, failed to enforce Section 2 of the Fourteenth Amendment, written to compel the Southern states to enfranchise blacks or lose representation. Finally, in 1929, after being unable to make a reapportionment of seats among the states after the census of 1920, Congress decided to cap the number of Representatives at 435.

Since 1790, Congress has applied five different methods of apportioning Representatives among the states. The present “Hill Method,” with its complex formula determining when a state may gain or lose a seat, has been in use since 1940. It has been twice challenged before the Supreme Court. In Franklin v. Massachusetts (1992), the Court upheld the inclusion of federal military and civil personnel and their dependents in the apportioned populations. In United States Department of Commerce v. Montana (1992), the Court unanimously approved the “Hill Method” in the face of a challenge by Montana, which had lost one seat in favor of Washington after the 1990 census.

Although under the Equal Protection Clause of the Fourteenth Amendment, the population for each Congressional district within each state must be the same, Wesberry v. Sanders (1964), populations of districts among the states do not have to be. State average district populations vary considerably from the national average. For example, after the 2000 Census, Wyoming had an average district population that was 23.44 percent smaller than the national average while Montana’s was 39.94 percent larger.

A federal court turned aside claims that, under this clause, allocating seats by voting age population, rather than numerical population, should be required. Kalson v. Paterson (2008). And the clause does not compel the government to treat Puerto Rico as a state for purposes ofm representation, for the clause only applies to actual states, not territories. Igartúa v. U.S. (2010).