Within the individual United States, bicameralism was usually modeled upon that of the United States Federal Government, with the upper house, in analogy to the states, consisting of State Senators who represented geographic areas independent of their population, typically counties.
In 1964, a U.S. Supreme Court decision in Reynolds v. Sims voided this arrangement as applied to states. In response to this most states replaced the fixed geographic boundaries with more flexible State Senatorial Districts, which are re-drawn after every decennial census. In such cases the term of office for the upper house will usually be longer and the number of seats lower than for the lower house. Like the districts of the lower house they are now subject to the process of gerrymandering, with boundaries manipulated to favor incumbents of both parties (as in California), or to favor the majority party (as in Maryland and Texas).
On November 6, 1934, Nebraska passed a constitutional amendment converting their bicameral system to the current unicameral system. US senator George W. Norris, an advocate for unicameralism, led the way with his efforts to promote and successfully implement the new legislative system.  Norris' criticisms of bicameralism still resonate today. Norris believed that:
- The conference committee system used by bicameral legislatures was tantamount to a third chamber and held all the real power, since disagreements between the House and Senate were usually resolved secretly by these committees. 
- Corrupt lobbyists manipulated the two-house system. 
- The legislature was supposed to be small in size and close to the people, in order to be the most responsive to the needs of the people. 
Michigan unicameral petition drive
An unsuccessful effort to collect petition signatures was launched in January 2006 by Unicameral Michigan, a ballot question committee registered with the State of Michigan, to provide for an amendment to the state's constitution to change from a bicameral to a unicameral legislature. It failed to qualify for the November 2006 ballot.