The NCSL Blog


By Wendy Underhill

What data must redistricters use when they go about their every-10-years task of creating equal population districts?

Census LogoThe short answer is, “Census data. Duh.”

That answer is correct for congressional districts: Data from the federal decennial census must be used. (See U.S. Constitution: Article I, Section 2, Clause 3.)

For legislative districts, it’s not quite so clear. Sure, in practice all the states have used census data for decades, but must they? NCSL’s Christi Zamarripa has dug in deep on this question and produced the webpage Redistricting and the Use of Census.

In it, you’ll see that 21 states explicitly require the use of federal census data for congressional and legislative redistricting; two more, Arkansas and Texas, are explicit about using the census for redistricting the state House but are not so clear about the Senate. Another 17 states imply that census data will be used.

New York and Ohio say that if, for some reason, the census data is unavailable or delayed, then the state can choose another source.

Hawaii requires federal census data be used for congressional reapportionment and congressional redistricting when practicable but is silent regarding state legislative redistricting.

Indiana explicitly requires that federal census data be used for legislative redistricting, but it does not use explicit language when addressing congressional redistricting.

Six states provide more leeway, but even these all refer to the federal census in a way that implies it’s the first choice for data:

  • Alabama (Alabama Const. Art. IX, Sec. 201): “Should any decennial census of the United States not be taken, or if when taken, the same, as to this state, be not full and satisfactory, the legislature shall have the power at its first session after the time shall have elapsed for the taking of said census, to provide for an enumeration of all the inhabitants of this state.”
  • Maine (Me. Const. Art. IV, Pt. 1, 2): "The number of Representatives shall be divided into the number of inhabitants of the State exclusive of foreigners not naturalized according to the latest Federal Decennial Census or a State Census previously ordered by the Legislature to coincide with the Federal Decennial Census.”>
  • Nevada (Nev. Const. Art. 15, 13): “The enumeration of the inhabitants of this State shall be taken under the direction of the Legislature if deemed necessary … and these enumerations, together with the census that may be taken under the direction of the Congress of the United States in A.D. Eighteen hundred and Seventy, and every subsequent ten years shall serve as the basis of representation in both houses of the Legislature.”
  • New Hampshire (N.H. Const. Pt. SECOND, Art. 9): “The legislature shall make an apportionment of representatives according to the last general census of the inhabitants of the state taken by authority of the United States or of this state.”
  • Oregon (Ore. Const. Art. IV, 6): Redistricting takes place “At the odd-numbered year regular session of the Legislative Assembly next following an enumeration of the inhabitants by the United States Government.”
  • South Carolina (S.C. Const. Ann. Art. III, 3): "The General Assembly may at any time, in its discretion, adopt the immediately preceding United States Census as a true and correct enumeration of the inhabitants of the several Counties.”

What the state constitutions do not address is which data from the census is to be used? Total population? Voting age population? Or Citizenship population data?

For that answer, we’ll need to wait and see.

Wendy Underhill is the director of NCSL's Elections and Redistricting Program.

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About the NCSL Blog

This blog offers updates on the National Conference of State Legislatures' research and training, the latest on federalism and the state legislative institution, and posts about state legislators and legislative staff. The blog is edited by NCSL staff and written primarily by NCSL's experts on public policy and the state legislative institution.