U.S. Department of Commerce

Economics and Statistics Administration

U.S. CENSUS BUREAU

C2010BR-08

Congressional Apportionment

2010 Census Briefs

Issued November 2011

By

Kristin D. Burnett

The Constitutional basis for conducting the decennial census of population is to reapportion the U.S. House of 

Representatives. Apportionment is the 

process of dividing the 435 memberships, or seats, in the U.S. House of 

Representatives among the 50 states. 

With the exception of the 1920 Census, 

an apportionment has been made by the 

Congress on the basis of each decennial 

census from 1790 to 2010.

The apportionment population for 2010 

consists of the resident population of the 

50 states plus overseas federal employees 

(military and civilian) and their dependents living with them, who were included 

in their home states. The population of 

the District of Columbia is excluded from 

the apportionment population because 

it does not have any voting seats in the 

U.S. House of Representatives. The 2010 

Census apportionment population was 

309,183,463, as shown in Table 1.1

This report examines trends in congressional apportionment and discusses the 

apportionment population—what it is, 

who is included, and what method is 

used to calculate it. The report is part of a 

series that analyzes population and housing data collected by the 2010 Census. 

1 The 2010 Census resident population of the 

United States, including the District of Columbia, was 

308,745,538.

The average size of a congressional 

district will rise. 

The number of representatives or seats 

in the U.S. House of Representatives has 

remained constant at 435 since 1911, 

except for a temporary increase to 437 

at the time of admission of Alaska and 

Hawaii as states in 1959 (see Table 1). 

However, the apportionment based on the 

1960 Census, which took effect for the 

election in 1962, reverted to 435 seats.

The average size of a congressional 

district based on the 2010 Census 

apportionment population will be 

710,767, more than triple the average 

district size of 210,328 based on the 

1910 Census apportionment, and 63,815 

more than the average size based on 

Census 2000 (646,952). Based on the 

2010 Census apportionment, the state 

with the largest average district size will 

be Montana (994,416), and the state with 

the smallest average district size will be 

Rhode Island (527,624).
2 U.S. Census Bureau

Table 1. 

Apportionment Population Based on the 2010 Census and Apportionment of the 

U.S. House of Representatives: 1910 to 2010 

(For information on confidentiality protection, nonsampling error, and definitions, see www.census.gov/prod/cen2010/pl94-171.pdf)

State

2010 apportionment population1 Number of representatives

Total

Resident 

population

U.S. 

population 

overseas 2010 2000 1990 1980 1970 1960 1950 1940 1930 19202 1910

 Total . . . . . . . . . . . . 309,183,463 308,143,815 1,039,648 435 435 435 435 435 435 3

437 435 435 435 4435

Alabama ................ 4,802,982 4,779,736 23,246 7 7 7 7 7 8 9 9 9 10 10

Alaska .................. 721,523 710,231 11,292 1 1 1 1 1 1 1 (X) (X) (X) (X)

Arizona ................. 6,412,700 6,392,017 20,683 9 8 6 5 4 3 2 2 1 1 1

Arkansas ................ 2,926,229 2,915,918 10,311 4 4 4 4 4 4 6 7 7 7 7

California ................ 37,341,989 37,253,956 88,033 53 53 52 45 43 38 30 23 20 11 11

Colorado ................ 5,044,930 5,029,196 15,734 7 7 6 6 5 4 4 4 4 4 4

Connecticut .............. 3,581,628 3,574,097 7,531 5 5 6 6 6 6 6 6 6 5 5

Delaware ................ 900,877 897,934 2,943 1 1 1 1 1 1 1 1 1 1 1

Florida .................. 18,900,773 18,801,310 99,463 27 25 23 19 15 12 8 6 5 4 4

Georgia ................. 9,727,566 9,687,653 39,913 14 13 11 10 10 10 10 10 10 12 12

Hawaii .................. 1,366,862 1,360,301 6,561 2 2 2 2 2 2 1 (X) (X) (X) (X)

Idaho ................... 1,573,499 1,567,582 5,917 2 2 2 2 2 2 2 2 2 2 2

Illinois ................... 12,864,380 12,830,632 33,748 18 19 20 22 24 24 25 26 27 27 27

Indiana .................. 6,501,582 6,483,802 17,780 9 9 10 10 11 11 11 11 12 13 13

Iowa .................... 3,053,787 3,046,355 7,432 4 5 5 6 6 7 8 8 9 11 11

Kansas .................. 2,863,813 2,853,118 10,695 4 4 4 5 5 5 6 6 7 8 8

Kentucky ................ 4,350,606 4,339,367 11,239 6 6 6 7 7 7 8 9 9 11 11

Louisiana ................ 4,553,962 4,533,372 20,590 6 7 7 8 8 8 8 8 8 8 8

Maine ................... 1,333,074 1,328,361 4,713 2 2 2 2 2 2 3 3 3 4 4

Maryland ................ 5,789,929 5,773,552 16,377 8 8 8 8 8 8 7 6 6 6 6

Massachusetts ............ 6,559,644 6,547,629 12,015 9 10 10 11 12 12 14 14 15 16 16

Michigan ................ 9,911,626 9,883,640 27,986 14 15 16 18 19 19 18 17 17 13 13

Minnesota ............... 5,314,879 5,303,925 10,954 8 8 8 8 8 8 9 9 9 10 10

Mississippi ............... 2,978,240 2,967,297 10,943 4 4 5 5 5 5 6 7 7 8 8

Missouri ................. 6,011,478 5,988,927 22,551 8 9 9 9 10 10 11 13 13 16 16

Montana ................. 994,416 989,415 5,001 1 1 1 2 2 2 2 2 2 2 2

Nebraska ................ 1,831,825 1,826,341 5,484 3 3 3 3 3 3 4 4 5 6 6

Nevada ................. 2,709,432 2,700,551 8,881 4 3 2 2 1 1 1 1 1 1 1

New Hampshire ........... 1,321,445 1,316,470 4,975 2 2 2 2 2 2 2 2 2 2 2

New Jersey .............. 8,807,501 8,791,894 15,607 12 13 13 14 15 15 14 14 14 12 12

New Mexico .............. 2,067,273 2,059,179 8,094 3 3 3 3 2 2 2 2 1 1 1

New York ................ 19,421,055 19,378,102 42,953 27 29 31 34 39 41 43 45 45 43 43

North Carolina ............ 9,565,781 9,535,483 30,298 13 13 12 11 11 11 12 12 11 10 10

North Dakota ............. 675,905 672,591 3,314 1 1 1 1 1 2 2 2 2 3 3

Ohio .................... 11,568,495 11,536,504 31,991 16 18 19 21 23 24 23 23 24 22 22

Oklahoma ............... 3,764,882 3,751,351 13,531 5 5 6 6 6 6 6 8 9 8 8

Oregon .................. 3,848,606 3,831,074 17,532 5 5 5 5 4 4 4 4 3 3 3

Pennsylvania ............. 12,734,905 12,702,379 32,526 18 19 21 23 25 27 30 33 34 36 36

Rhode Island ............. 1,055,247 1,052,567 2,680 2 2 2 2 2 2 2 2 2 3 3

South Carolina ............ 4,645,975 4,625,364 20,611 7 6 6 6 6 6 6 6 6 7 7

South Dakota ............. 819,761 814,180 5,581 1 1 1 1 2 2 2 2 2 3 3

Tennessee ............... 6,375,431 6,346,105 29,326 9 9 9 9 8 9 9 10 9 10 10

Texas ................... 25,268,418 25,145,561 122,857 36 32 30 27 24 23 22 21 21 18 18

Utah .................... 2,770,765 2,763,885 6,880 4 3 3 3 2 2 2 2 2 2 2

Vermont ................. 630,337 625,741 4,596 1 1 1 1 1 1 1 1 1 2 2

Virginia .................. 8,037,736 8,001,024 36,712 11 11 11 10 10 10 10 9 9 10 10

Washington .............. 6,753,369 6,724,540 28,829 10 9 9 8 7 7 7 6 6 5 5

West Virginia ............. 1,859,815 1,852,994 6,821 3 3 3 4 4 5 6 6 6 6 6

Wisconsin ............... 5,698,230 5,686,986 11,244 8 8 9 9 9 10 10 10 10 11 11

Wyoming ................ 568,300 563,626 4,674 1 1 1 1 1 1 1 1 1 1 1

(X) Not applicable.

1

 Includes the resident population for the 50 states, as ascertained by the 2010 Census under Title 13, U.S. Code, and counts of overseas U.S. military and 

federal civilian employees (and their dependents living with them) allocated to their home state, as reported by the employing federal agencies. The apportionment 

population does not include the resident or the overseas population of the District of Columbia. 2

 No reapportionment was made based on the 1920 Census.

3

 The 1950 apportionment originally resulted in the previously fixed House size of 435 representatives; but in 1959, Alaska and Hawaii were both newly admitted 

to the United States, and each was granted one representative—temporarily increasing the size of the House to 437. Then the 1960 apportionment reverted back to 

the fixed size of 435. 4

 The apportionment act following the 1910 Census was passed on August 8, 1911. This congressional act (U.S. Statutes at Large, Pub.L. 62-5, 37 Stat. 13) 

fixed the size of the House at 433 representatives, with a provision for the addition of one seat each for Arizona and New Mexico when they would become states 

the following year. The resulting House size, 435 members, has been unchanged since, except for a temporary increase to 437 at the time of admission of Alaska 

and Hawaii as states (see footnote 3).

Sources: U.S. Census Bureau, 2010 Census at <www.census.gov/population/apportionment/data>; and 2000 Census of Population and Housing, Population 

and Housing Unit Counts, United States Summary: 2000 (PHC-3-1, Part 1), Table 3.
U.S. Census Bureau 

3

Figure 1.Apportionment of the U.S. House of Representatives Based on the 2010 

AK

1

WA

10

OR

5

CA

53

NV

4

ID

2

MT

1

WY

1

UT

4 CO

7

AZ

9 NM3

ND

1

SD

1

NE

3

KS

4

OK

5

TX

36

MN

8

IA

4

MO

8

AR

4

LA

6

WI

8

IL

18

IN

9

MI

14

OH

16

KY

6

TN

9

MS

4

AL

7

GA

14

FL

27

SC

7

NC

13

VA

11

WV

3

PA

18

ME

2

NH

2

VT

1

NY

27

HI

2

MA 

RI 

CT 

NJ 12

DE 1

MD 8

WEST

REGION MIDWEST

REGION

SOUTH

REGION

Change from 

State State State No cState State 

Numbers retotals of U.S

Cens

Total U.S. R

(For information on confidentiality protection, nonsampling error, and definitions, see www.census.go

/cen2010/doc/sf1.pdf)

Sources: U.S. Census Bureau, 2010 Census and Census 2000 at <www.census.gov/population/apportionment/data>.
4 U.S. Census Bureau

Twelve seats in the U.S. House 

of Representatives will shift 

from one state to another.

As a result of the apportionment based on the 2010 Census, 

12 seats in the U.S. House of 

Representatives will shift among 

18 states. Eight states will have 

more representatives in the 113th 

Congress, which convenes in 

January 2013, and ten states will 

have fewer representatives (see 

Figure 1 and Table 2). 

Among the eight states gaining 

seats, Texas will gain four seats 

and Florida will gain two seats. 

The other six states (Arizona, 

Georgia, Nevada, South Carolina, 

Utah, and Washington) will each 

gain one seat.

Of the ten states losing seats, 

two states, New York and Ohio, 

will each lose two seats. The 

other eight states (Illinois, 

Iowa, Louisiana, Massachusetts, 

Michigan, Missouri, New Jersey, 

and Pennsylvania) will each lose 

one seat.

The Census 2000 

apportionment also 

shifted 12 seats.

The seat changes that will occur 

based on the 2010 Census show 

many parallels to the seat changes 

that occurred after Census 2000. 

For example, the 2000-based 

reapportionment also led to a shift 

of 12 seats among 18 states (see 

Table 2). 

Five of the eight states that will 

gain seats following the 2010 

Census also gained seats following Census 2000: Arizona, Florida, 

Georgia, Nevada, and Texas. 

Similarly, five of the ten states that 

will lose seats following the 2010 

Census also lost seats following 

Census 2000: Illinois, Michigan, 

New York, Ohio, and Pennsylvania.

Sources: U.S. Census Bureau, 2010 Census and Census 2000 at <www.census.gov/population 

/apportionment/data>.

Shifts in congressional Similar regional shifts occurred 

representation reflect regional after Census 2000. At that time, 

trends in population. the net increase of five seats in 

The regional patterns of change the South reflected a gain of 

in congressional representation seven seats in four states and a 

between 2000 and 2010 reflect loss of two seats. The West gained 

the nation’s continuing shift in five seats across four states and 

population from the Northeast and lost none. The Northeast and 

Midwest to the South and West. Midwest each lost five seats and 

gained none.

Based on the 2010 Census apportionment, the net increase of seven Figure 2 shows the percentage 

seats in the South reflected a gain distribution of House seats or 

of eight seats across four states memberships by region for each 

and a loss of one seat (see Figure 1 census since 1910. In 1910, the 

and Table 3). The West gained four West held the smallest share of 

seats and lost none. The Northeast House seats out of the four regions 

lost five seats and gained none. (33 seats, or 7.6 percent), but it 

The Midwest lost six seats and steadily increased each decade, 

gained none. more than tripling in seats by 2010 

(102 seats, or 23.4 percent). After 

the 1990 apportionment, the West 

Table 2. 

Change in the Number of U.S. Representatives by State: 

2000 and 2010

(For information on confidentiality protection, nonsampling error, and 

definitions, see www.census.gov/prod/cen2010/pl94-171.pdf)

State Gain State Loss

BASED ON 2010 CENSUS BASED ON 2010 CENSUS

Total gain in 8 states . . . . . . . . . . . . . 12 Total loss in 10 states . . . . . . . . . . 12

Texas .......................... 4 New York ..................... 2

Florida ......................... 2 Ohio ......................... 2

Arizona ........................ 1 Illinois ........................ 1

Georgia ........................ 1 Iowa ......................... 1

Nevada ........................ 1 Louisiana ..................... 1

South Carolina ................... 1 Massachusetts ................. 1

Utah ........................... 1 Michigan ..................... 1

Washington ..................... 1 Missouri ...................... 1

New Jersey ................... 1

Pennsylvania .................. 1

BASED ON CENSUS 2000 BASED ON CENSUS 2000

Total gain in 8 states . . . . . . . . . . . . . 12 Total loss in 10 states . . . . . . . . . . 12

Arizona ........................ 2 New York ..................... 2

Florida ......................... 2 Pennsylvania .................. 2

Georgia ........................ 2 Connecticut ................... 1

Texas .......................... 2 Illinois ........................ 1

California ....................... 1 Indiana ....................... 1

Colorado ....................... 1 Michigan ..................... 1

Nevada ........................ 1 Mississippi .................... 1

North Carolina ................... 1 Ohio ......................... 1

Oklahoma .................... 1

Wisconsin .................... 1
U.S. Census Bureau 5

Table 3.

Change in the Number of U.S. Representatives by Region: 

2000 and 2010

(For information on confidentiality protection, nonsampling error, and definitions, 

see www.census.gov/prod/cen2010/pl94-171.pdf)

Region Gain Loss Net

BASED ON 2010 CENSUS

Northeast ..............................

Midwest ...............................

South .................................

West .................................

–

–

8

4

5

6

1

–

–5

–6

7

4

BASED ON CENSUS 2000

Northeast ..............................

Midwest ...............................

South .................................

West .................................

–

–

7

5

5

5

2

–

–5

–5

5

5

– Represents zero.

Sources: U.S. Census Bureau, 2010 Census and Census 2000 at <www.census.gov/population 

/apportionment/data>.

(93 seats, or 21.4 percent) surpassed the Northeast (88 seats, or 

20.2 percent) in share of seats for 

the first time; and after the 2010 

apportionment, the West (102 

seats, or 23.4 percent) will surpass 

the Midwest (94 seats; 21.6 percent) for the first time.

The South’s share of House seats 

held relatively firm from 1910 to 

1970 at about 31 percent (between 

133 and 136 seats), and then it 

increased to 37.0 percent (161 

seats) by 2010. After the 2010 

apportionment, the South will 

maintain the largest share of House 

seats among all four regions, as it 

has since 1940. 

Figure 2.

Percentage Distribution of Seats in the U.S. House of Representatives by Region: 

1910 to 2010

Sources: U.S. Census Bureau, 2010 Census at <www.census.gov/population/apportionment>; and 2000 Census of Population and Housing,

Population and Housing Unit Counts, United States Summary (PHC-3-1, Part 1), Table 3.

(For information on confidentiality protection, nonsampling error, and definitions, see www.census.gov/prod

/cen2010/pl94-171.pdf)

Northeast

Midwest

South

West

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

32.9 32.9 31.5 30.1 29.5 28.7 27.8 26.0 24.1 23.0

21.6

31.3 31.3 30.6 31.0 30.7

30.6

30.8

32.6 34.3 25.4

37.0

7.6 7.6 9.9 11.3 13.5 15.9 17.5 19.5 21.4 22.5 23.4

28.3 28.3 28.0 27.6 26.3 24.8 23.9 21.8 20.2 19.1 17.9
6 U.S. Census Bureau

Meanwhile, the Midwest, which Step 2: Calculate a list of are calculated in a similar fashion. 

accounted for the largest regional priority values. Then the same process is repeated 

share of House seats in 1910 for each of the other states. A “priority value” is based on a through 1930 (between 137 and state’s apportionment population 143 seats, or between 31.5 and Step 3: Assign the remaining and the number of its next poten- seats in ranked order. 32.9 percent), showed a steady tial seat. More specifically, the for- decline to 21.6 percent (94 seats) mula for a priority value (PV) equals After all of the states’ priority valby 2010. the state’s apportionment popula- ues have been calculated, a comtion divided by the geometric mean bined list of priority values from After holding relatively stable at 

of its current (n–1) and next (n) every state is ranked in descending about 28 percent (between 120 

potential seat number. order. The state with the largest and 123 seats) from 1910 to 1940, 

the Northeast’s share of House 

seats gradually decreased to only 

17.9 percent (78 seats) by 2010. 

����� � � ����������

�

���������

� � �� � ��

���������� priority value in the list is given 

the 51st seat (because the first 50 

seats are automatically assigned); 

then the state with second largest Therefore, after the 2010 appor- Because every state automatically priority value is given the 52nd tionment, the Northeast will hold receives its first seat, priority val- seat. This process is continued for the smallest share of House seats ues start with each state’s second each consecutively descending among all four regions, as it has seat. The maximum number of pri- priority value until the last (435th) since 1990. ority values ever needed for each seat has been filled. The state 

state would account for the hypo- composition of the reapportioned CALCULATING thetical situation in which one state APPORTIONMENT House of Representatives is then 

is so large that it receives all of the complete.

Congress decides the method final 385 seats that remain after the 

to calculate apportionment. first 50 are automatically assigned. ADDITIONAL TOPICS 

This means one could potentially ON CONGRESSIONAL The process of apportionment calculate a total list of 19,250 APPORTIONMENT determines the distribution of conpriority values (385 PVs multiplied gressional seats among the states. When are the apportionment by 50 states). In general, however, Several apportionment methods population counts given to the it is more efficient to only calculate have been used since the first President? To the Congress? enough priority values to account census in 1790. The apportionment To the states? 

for the largest number of seats any for the 2010 Census was calcu- To the President. Title 13, U.S. Code particular state might currently lated using the method of equal requires that the apportionment be assigned (or proportionate to proportions, in accordance with the population counts for each state be each state’s actual population). provisions of Title 2, U.S. Code. The delivered to the President within 9 For example, one may choose to method of equal proportions has months of Census Day, which was calculate approximately 60 prior- been used for apportionment after April 1, 2010. The 2010 Census ity values for each state because every census since 1940. counts were delivered to the the most populous state in Census President on December 21, 2010. 2000 received 53 seats. Step 1: Automatically assign 

the first 50 seats. To the Congress. According to In practice, the priority values for Title 2, U.S. Code, within 1 week First, each state is assigned one a specific state’s second and third of the opening of the next ses- congressional seat, as provided by seats in the 2010 Census are comsion of the Congress in the new the Constitution. Then, in the fol- puted as follows. Using Alabama as year, the President must report lowing steps, the method of equal the example state:

proportions allocates the remaining 

385 congressional seats among the ���2�������������������� � 4,8

√

0

2��

2,982 �,22�

to the Clerk of the U.S. House of 

-

� Repr

50 states, according to their appor

�,�9 esentatives the apportionment 

population counts for each state 

and the number of representatives tionment populations. ������������������������ � 4,802,982

√��2

� �,9�0,809

to which each state is entitled. The 

President sent the 2010 apporThe rest of the priority values for tionment results to the House on 

all of Alabama’s potential seats January 5, 2011. 

���2�������������������� � 4,802,982

√2��

� �,�9�,22�

������������������������ � 4,802,982

√��2

� �,9�0,809

����� � � ������������������������������

�� � �� � ��
U.S. Census Bureau 7

To the States. Also according to Were undocumented residents released the redistricting populaTitle 2, U.S. Code, within 15 days of in the 50 states included in the tion data at the census block level 

2010 Census apportionment receiving the apportionment popu- on a state-by-state basis during population counts? lation counts from the President, February and March 2011.

the Clerk of the House must inform All people (citizens and noncitieach state governor of the number zens) with a usual residence in one FOR MORE INFORMATION 

of representatives to which each of the 50 states were included in For more information on apportion- state is entitled. The 2010 appor- the 2010 Census and thus in the ment for both the 2010 and 2000 

tionment results were transmitted apportionment counts. This has censuses, visit the U.S. Census 

to all the states by January 18, been true since the first census Bureau’s Internet site at 

2011. in 1790. <www.census.gov/population 

/apportionment>. Data from the Were children under 18 What is the difference 2010 Census are available on the years old included in the between apportionment and Internet at <http://factfinder2 2010 Census apportionment redistricting? 

population counts even though .census.gov> and on DVD. 

Population data from the decen- they cannot vote? Information on confidentiality 

nial census provide the basis for protection, nonsampling error, and Yes. Being old enough to vote, both apportioning House seats definitions is available at being registered to vote, or actu- among the states and for redistrict- <www.census.gov/prod/cen2010 ally voting are not requirements ing the legislative bodies within /doc/pl94-171.pdf>. for inclusion in the apportionment each state. Apportionment is the 

counts. process of determining the number Information on other population 

of representatives to which each and housing topics is presented 

Did the 2010 Census state is entitled in the U.S. House in the 2010 Census Briefs series, apportionment population of Representatives based on the located on the Census Bureau’s Web counts include all Americans 

decennial census. Wher site at <www.census.gov/prod overseas? eas, redistricting is the process of revising /cen2010>. This series will present 

The overseas portion of the the geographic boundaries of areas information about race, Hispanic 

2010 apportionment counts only from which people elect repre- origin, age, sex, household type, 

included overseas federal employ- sentatives to the U.S. House of housing tenure, and people who 

ees (military and civilian) and Representatives, a state legislature, reside in group quarters.

their dependents living with them. a county or city council, a school Private U.S. citizens living abroad For more information about the 

board, and so forth. By law (PL who were not employees of the 2010 Census, including data prod- 94-171), redistricting data must be federal government (or their depen- ucts, call our Customer Services submitted to the states within one 

dents) were not included in the Center at 301-763-INFO or at 

year of the census date (so, for this overseas counts. 1-800-923-8282. You can also visit 

decade, redistricting data had to be our Question and Answer Center at submitted to states by no later than <ask.census.gov> to submit your April 1, 2011). The Census Bureau questions online.