The federal legislature in the USA is bicameral, with the Senate (supposedly) representing states, with equal voting power among state, and the House of Representatives (supposedly) representing the people, with voting power distributed by population size. See:

Why does the US Congress have two chambers?

But then - why have individual states set up bicameral legislatures? The same consideration does not seem to exist on the state level.

Note: I'm not asking whether this is better or worse, but rather about the official, ideological, rationale for this structure.

2 Answers 2


In the US, state and local legislatures can choose to be bicameral, unicameral or something else. As of today, all state legislatures are bicameral, except in Nebraska, which is unicameral.

Most local governments are unicameral.

The US Congress has no structural flexibility. It must be bicameral, as mandated by the Constitution.

Why are most state legislatures bicameral?

It appears to be a vestige of colonial governments:

Before the Revolution, most individual colonies had followed the bicameral model in their governments, with an upper house, generally called the council, representing the interests of the proprietor or the Crown, and a lower house, generally called the assembly, representing the settlers.

source: encyclopedia.com

Why are most local legislatures unicameral?

On the local level, bicameral legislatures were most common until the reform movement at the turn of the twentieth century made unicameral city councils the norm by the 1930s.

While distrust of the masses and the "need" for a propertied elite to guide them has clearly vanished as an argument for a bicameral system, this is not reflected in the set-up of the legislatures at the state or federal levels.

source: encyclopedia.com

Why is the US Congress bicameral?

The answer is pretty well summarized in the post referenced in the question:

Here's an excerpt from the accepted answer:

The U.S. Congress didn't actually start out bicameral; the original Articles of Confederation (the pre-Constitution) had a single house. The final Constitution split Congress into the House and Senate as a compromise between the large states (who naturally wanted representation to be tied to population) and the small states (who didn't want to get outvoted all day long by the larger states). Rather than pick one, they made two houses, one with representation by population and one with equal representation for each state.

I'll add this from another source, which is a bit more detailed:

The first organizational law of the United States, the Articles of Confederation of 1781, prescribed a unicameral Congress.

This changed when delegates met at the Constitutional Convention in the summer of 1787. They adopted Edmund Randolph's plan for a three-branch government and a bicameral legislature based on population after a weeklong debate dismissing an alternative proposal by William Paterson of New Jersey for a unicameral legislature in which each state would have one vote.

Paterson's plan had been supported by the smaller states, which feared that a legislature apportioned according to population would lead to dominance by the larger states.

Distrusting democracy, many of the delegates were afraid that in a single house only the members' "virtue and good sense" would prevent legislative despotism. This seemed an inadequate check. The only possible restraint was to divide the legislative authority within itself.

Ideas about an upper house, where men of property and great wisdom would take care of issues that were beyond the grasp of the masses, merged with the need to find a compromise that would provide the smaller states with a satisfactory input in the legislative process.

Accordingly the convention compromised to propose a House of Representatives, in which members were apportioned among the states according to population, and a Senate, in which each state had an equal vote.

source: encyclopedia.com

Side note: Interesting to read how the founding fathers created the US Congress, in part, based on their distrust of democracy:

Distrusting democracy, many of the delegates were afraid that in a single house only the members' "virtue and good sense" would prevent legislative despotism.

That issue ties into this post: When is a democratic vote actually the wrong tool?

  • Suggest you remove the section about the federal legislature, as that's already linked to in the question.
    – einpoklum
    Feb 18, 2018 at 17:00
  • I put it last, just to provide a complete answer, with all three levels of government covered. I've also added some detail that's not present in the referenced post. Feb 18, 2018 at 17:02
  • "The US Congress has no structural flexibility. It must be bicameral, as mandated by the Constitution": this applies to most state legislatures if not all of them. Their structure is also generally mandated by the state constitution. Or, to look at it another way, just as a state can change its constitution to modify the way its legislature is, well, constituted, so can the federation.
    – phoog
    Apr 9, 2019 at 21:22
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    There is also a functional consideration. Bicameralism slows down the legislative process, allows more opportunities for public input before legislation is a fait accompli, forces more attention to details because chamber come up with non-identical versions of legislation, and strengthens the need for bipartisan compromise when the legislative chambers are split between parties which tends to happen when both parties have roughly the same amount of support subject to random variation. It tends to prevent thin majorities from overreaching in a manner similar to supermajority requirements.
    – ohwilleke
    Apr 10, 2019 at 22:34
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    @ohwilleke, it's possible you are correct. My answer is based on a few hours of research from several online sources which may just be parroting each other. A deep dive into the subject may yield more accurate and more meaningful information. Consider posting an answer or editing mine. Apr 11, 2019 at 22:23

County-based districts

The same consideration does not seem to exist on the state level.

While that is true now, it did not used to be true. Prior to the court case Reynolds v. Sims, it was not strange for states to base one of their chambers on counties. So each county would get a fixed number of representatives (e.g. one) much the way the federal Senate gets two per state. I don't know how many states had county-districted chambers, but at least thirteen are listed on Wikipedia.

Balancing the power of rural and urban counties was in fact a specific reason for a second, senatorial chamber in many states.

As county-based districts were removed by judicial fiat rather than democratic processes, most states kept their second chambers, even if the original justification no longer applied.


At least one state, Washington, has things set up so that each state Senate district is comprised of two state Representative districts. This makes redistricting less impactful, as even if a Representative district ends up out of pace, when paired with a second neighboring district, it will tend to revert towards the mean.


Three of the thirteen original colonies were unicameral when the United States started in 1789. Georgia, Pennsylvania, and Vermont switched to be bicameral afterwards. I've seen a discussion of why they did so, but I don't remember where. I'll add it if I see it again.

It may be worth noting that the Articles of Confederation had a unicameral legislature but were supplanted by the constitution when the confederation was found to be too unwieldy.

  • One of the few requirements for statehood is a Republic Form of Government as approved of by Congress. This gives states a wide range of options for government, but even some Democratic Governments like the United Kingdom are flat out (No Royalty) and possibly Japan (The Emporer is purely a symbolic figure and has no government authority, as opposed to the Queen of England, who does have some government functions (like abolishing Parliment). While no state may be a pure direct democracy, they may be semi-direct and all 50 states do have some form of Semi-Direct Democracy.
    – hszmv
    Feb 21, 2018 at 15:05
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    @hszmv there has not been a queen of England since Queen Anne, who ceased to be Queen of England when the Kingdom of England ceased to exist on 1 May 1707.
    – phoog
    Apr 9, 2019 at 21:26

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