U.S. Department of Commerce

Economics and Statistics Administration

U.S. CENSUS BUREAU

Household Income Inequality 

Within U.S. Counties: 2006–2010

American Community Survey Briefs

By

Adam Bee 

ACSBR/10-18

Issued February 2012

Household income: Includes pretax money income of the householder and all other people 15 

years and older in the household, 

whether or not they are related to 

the householder.

Gini index: Summary measure of 

income inequality. The Gini index 

varies between zero and one. A 

value of one indicates perfect 

inequality where only one household has any income. A value of 

zero indicates perfect equality, 

where all households have equal 

income.

Since 1967, U.S. household income 

inequality has grown 18 percent. Nearly 

half of that growth occurred during the 

1980s. More recently, the growth in 

income inequality has tapered off.1 Levels 

of inequality vary across the country. This 

report presents measures of household 

income inequality for counties in the 

United States, based on data pooled from 

5 years (2006 to 2010) of American 

Community Survey (ACS) data.2 

The ACS surveys households in each 

month from January to December. It asks 

about income received during the previous 12 months. Each year’s survey covers 

23 months, from January of the previous 

year to November of the survey year. In 

total, the 5-year ACS used in this report 

covers the 71-month period from January 

2005 through November 2010. Pooling 

data allows more accurate measurement 

of inequality in less populous counties.

Figure 1 illustrates each county’s level of 

income inequality, as measured by the 

Gini index. The 5-year 2006–2010 Gini 

index for the United States as a whole 

was 0.467. County-level Gini indexes 

ranged from 0.645 to 0.207.

The South had a disproportionately large 

number of counties with high income 

1 DeNavas-Walt, Carmen, Bernadette D. Proctor, 

and Jessica C. Smith. 2011. “Income, Poverty, and 

Health Insurance Coverage in the United States: 

2010.” Table A-3: Selected Measures of Household 

Income Dispersion, 1967 to 2010. 2 In this report, the term “county” is used to refer 

to counties and statistically equivalent entities. This 

includes parishes, boroughs, municipalities, census 

areas, independent cities, the District of Columbia, 

and historical counties. For details see <www.census

.gov/geo/www/2010census/GTC_10.pdf> and 

<www.itl.nist.gov/fipspubs/fip6-4.htm>. 

inequality, while counties in the Midwest 

had lower levels of income inequality.3

Specifically, 32 percent of the 1,423 

counties in the South had Gini indexes 

ranking among the top fifth of all 3,143 

U.S. counties. By contrast, 31 percent of 

the 1,055 counties in the Midwest had 

Gini indexes in the bottom fifth (Table 1). 

Table 2 shows that the more unequal 

counties were also more populous. 

Thirty-four percent of Americans lived 

3 The South region includes Alabama, Arkansas, 

Delaware, the District of Columbia, Florida, Georgia, 

Kentucky, Louisiana, Maryland, Mississippi, North 

Carolina, Oklahoma, South Carolina, Tennessee, 

Texas, Virginia, and West Virginia. The Midwest 

consists of Illinois, Indiana, Iowa, Kansas, Michigan, 

Minnesota, Missouri, Nebraska, North Dakota, Ohio, 

South Dakota, and Wisconsin. The West region is 

Alaska, Arizona, California, Colorado, Hawaii, Idaho, 

Montana, Nevada, New Mexico, Oregon, Utah, 

Washington, and Wyoming. The Northeast is 

Connecticut, Maine, Massachusetts, New Hampshire, 

New Jersey, New York, Pennsylvania, Rhode Island, 

and Vermont.
2 U.S. Census Bureau 0 200 mi 0 400 km 0 300 km 0 150 mi 0 300 mi 0 600 km Figure 1. Quintiles of Gini Index by County: 2006-2010 Source: U.S. Census Bureau, 2006-2010 American Community Survey. For information on confidentiality protection, sampling error, nonsampling error, and definitions, see www. census.gov/acs/www .. Gini Index .461 to .645 .439 to .460 .422 to .438 .402 to .421 .207 to .401 Figure 1. Quintiles of Gini Index by County: 2006–2010 < >
U.S. Census Bureau 3

in a county that ranked in the top 

20 percent of U.S. counties by Gini 

index. In every region, the counties 

in the most unequal fifth of 

U.S. counties accounted for a disproportionately large share of that 

region’s population. For example, 

only 8 percent of Midwestern 

counties had Gini indexes ranking 

among the top fifth of U.S. counties, but they contained 26 percent 

of the region’s population.

While Tables 1 and 2 describe the 

national distribution of Gini indexes 

across counties, Table 3 considers 

the national distribution of countylevel Gini indexes across people. 

Specifically, Table 3 shows the proportions of each region’s population 

that ranked in each quintile of the 

national distribution of county-level 

Gini indexes across people. For 

example, the entry in the first row 

and the first column means that 17 

percent of Westerners were among 

the top fifth of Americans with the 

highest county-level Gini indexes. 

This table reflects the same pattern 

as shown in Tables 1 and 2 above. 

Southerners disproportionately 

lived in more unequal counties than 

other Americans, while Midwesterners disproportionately lived 

in more equal counties than their 

compatriots.

For the 25 most populous counties in the nation, Table 4 lists 

their Gini indexes and the largest 

cities within their metropolitan 

statistical areas (MSA). These 25 

counties contained 21 percent of 

the U.S. population.4 Nearly all 

were above the median county Gini 

index of 0.430; two major exceptions were San Bernardino County, 

CA, and Suffolk County, NY. San 

Bernardino County is the largest 

county by area in the contiguous 

4 Source: U.S. Census Bureau, 2010 

Census.

United States, stretching from the 

western suburbs of Los Angeles to 

the eastern border of California. 

Suffolk County consists of the eastern two-thirds of Long Island. As 

such, these counties include more 

sparsely populated areas than other 

counties in this list.

Table 1.

Distribution of County Gini Indexes for Regions: 

2006–2010

Distribution West South Midwest Northeast

U.S. 

overall

Number of counties. . . . . . . . . . . . . . . 448 1,423 1,055 217 3,143

Proportion of counties ranking in:

Top fifth of U.S. counties. . . . . . . . . . 0.12 0.32 0.08 0.12 0.20

2nd-highest fifth of U.S. counties. . . 0.21 0.25 0.13 0.18 0.20

Middle fifth of U.S. counties. . . . . . . 0.22 0.18 0.19 0.24 0.20

2nd-lowest fifth of U.S. counties. . . . 0.19 0.14 0.29 0.32 0.20

Bottom fifth of U.S. counties. . . . . . . 0.26 0.11 0.31 0.13 0.20

Total. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 1.00 1.00 1.00 1.00

Note: Totals may not sum exactly due to rounding.

Source: U.S. Census Bureau, 2006–2010 American Community Survey. 

Table 2.

Distribution of County Gini Indexes for Regions, Weighted 

by Population: 2006–2010

Distribution West South Midwest Northeast

U.S. 

overall

Population (millions). . . . . . . . . . . . . . . 72.3 114.4 67.0 55.4 309.1

Proportion of population residing in:

Top fifth of U.S. counties. . . . . . . . . . . 0.23 0.45 0.26 0.36 0.34

2nd-highest fifth of U.S. counties. . . . 0.42 0.23 0.22 0.22 0.27

Middle fifth of U.S. counties. . . . . . . . 0.19 0.14 0.17 0.19 0.17

2nd-lowest fifth of U.S. counties. . . . . 0.11 0.09 0.18 0.18 0.13

Bottom fifth of U.S. counties. . . . . . . . 0.05 0.09 0.17 0.04 0.09

Total. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 1.00 1.00 1.00 1.00

Note: Totals may not sum exactly due to rounding.

Sources: U.S. Census Bureau, 2006–2010 American Community Survey and 2010 Census 

(Population). 

Table 3.

Distribution of Region Population by County Gini Index 

Quintile: 2006–2010 

Distribution West South Midwest Northeast

U.S. 

overall

Population (millions). . . . . . . . . . . . . . . . 72.3 114.4 67.0 55.4 309.1

Proportion of people ranking in:

Top fifth of U.S. population. . . . . . . . . . 0.17 0.25 0.12 0.23 0.20

2nd-highest fifth of U.S. population. . . 0.13 0.25 0.20 0.18 0.20

Middle fifth of U.S. population. . . . . . . 0.34 0.16 0.15 0.16 0.20

2nd-lowest fifth of U.S. population. . . . 0.22 0.16 0.21 0.24 0.20

Bottom fifth of U.S. population. . . . . . . 0.14 0.18 0.32 0.18 0.20

Total. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 1.00 1.00 1.00 1.00

Note: Totals may not sum exactly due to rounding.

Sources: U.S. Census Bureau, 2006–2010 American Community Survey and 2010 Census 

(Population). 
4 U.S. Census Bureau

Table 5 lists counties among the 

highest and lowest estimated Gini 

indexes.5 Many of the counties with 

low Gini indexes were either very 

low in population or a fast-growing 

county containing commuter towns 

within a large metropolitan area. 

Loving County, TX, is an example 

of the former kind of county; it had 

both the lowest population in the 

country as well as the lowest Gini 

index estimate. Kendall County, 

IL, near Chicago, is an example of 

the latter kind; it had the highest 

population growth rate between 

the 2000 and 2010 Censuses, more 

than doubling over that decade.

SOURCE AND ACCURACY

Data presented in this report are 

based on people and households 

that responded to the ACS in years 

2006 through 2010. The resulting 

estimates are representative of the 

entire population. All comparisons 

presented in this report have taken 

sampling error into account and are 

significant at the 90 percent 

confidence level unless otherwise 

noted. Due to rounding, some 

details may not sum to totals. For 

information on sampling and 

estimation methods, confidentiality 

protection, and sampling and 

nonsampling errors, please see the 

“2010 ACS Accuracy of the Data” 

document located at <www.census

.gov/acs/www/Downloads

/data_documentation/Accuracy

/ACS_Accuracy_of_Data_2010.pdf>.

5 Few of the highest estimated Gini 

indexes are statistically significantly different from one another, and none of the 

lowest estimated Gini indexes is statistically 

significantly different from any other. The 

Gini index estimate for Franklin County, MS, 

is not statistically significantly different from 

the next highest estimated Gini index, and 

the estimate for Manassas Park city, VA, is not 

statistically significantly different from the 

next lowest estimated Gini index. The counties listed are intended as typical examples 

of counties with relatively high and low Gini 

indexes, respectively.

Table 4.

Gini Indexes for the 25 Most Populous Counties

Population 

rank County Population 

(2010)

Largest city 

of MSA

Estimated 

Gini index 

(2006–

2010)

1 Los Angeles County, California. . . . . . 9,818,605 Los Angeles 0.489

2 Cook County, Illinois. . . . . . . . . . . . . . 5,194,675 Chicago 0.488

3 Harris County, Texas. . . . . . . . . . . . . . 4,092,459 Houston 0.488

4 Maricopa County, Arizona. . . . . . . . . . 3,817,117 Phoenix 0.452

5 San Diego County, California. . . . . . . . 3,095,313 San Diego 0.452

6 Orange County, California. . . . . . . . . . 3,010,232 Los Angeles 0.455

7 Kings County, New York. . . . . . . . . . . . 2,504,700 New York 0.499

8 Miami-Dade County, Florida. . . . . . . . 2,496,435 Miami 0.503

9 Dallas County, Texas. . . . . . . . . . . . . . 2,368,139 Dallas 0.492

10 Queens County, New York. . . . . . . . . . 2,230,722 New York 0.433

11 Riverside County, California. . . . . . . . 2,189,641 Riverside 0.439

12 San Bernardino County, California. . . 2,035,210 Riverside 0.422

13 Clark County, Nevada. . . . . . . . . . . . . 1,951,269 Las Vegas 0.434

14 King County, Washington. . . . . . . . . . . 1,931,249 Seattle 0.456

15 Wayne County, Michigan. . . . . . . . . . . 1,820,584 Detroit 0.469

16 Tarrant County, Texas. . . . . . . . . . . . . 1,809,034 Dallas 0.448

17 Santa Clara County, California. . . . . . 1,781,642 San Francisco 0.450

18 Broward County, Florida. . . . . . . . . . . 1,748,066 Miami 0.469

19 Bexar County, Texas. . . . . . . . . . . . . . 1,714,773 San Antonio 0.463

20 New York County, New York. . . . . . . . . 1,585,873 New York 0.601

21 Philadelphia County, Pennsylvania. . . 1,526,006 Philadelphia 0.494

22 Alameda County, California. . . . . . . . . 1,510,271 San Francisco 0.456

23 Middlesex County, Massachusetts. . . 1,503,085 Boston 0.461

24 Suffolk County, New York. . . . . . . . . . . 1,493,350 New York 0.417

25 Sacramento County, California. . . . . . 1,418,788 Sacramento 0.431

Sources: U.S. Census Bureau, 2006–2010 American Community Survey and 2010 Census 

(Population). 

Table 5.

Counties Among the Highest and Lowest Levels of Income 

Inequality: 2006–2010

County Estimated Gini index

(2006–2010)

East Carroll Parish, Louisiana. . . . . . . . . . . . . 0.645

Edwards County, Texas. . . . . . . . . . . . . . . . . . 0.626

New York County, New York. . . . . . . . . . . . . . . 0.601

Mineral County, Colorado. . . . . . . . . . . . . . . . 0.598

Pitkin County, Colorado. . . . . . . . . . . . . . . . . . 0.591

Allendale County, South Carolina. . . . . . . . . . 0.582

Greene County, Georgia. . . . . . . . . . . . . . . . . 0.564

Randolph County, Georgia. . . . . . . . . . . . . . . 0.558

Sioux County, North Dakota. . . . . . . . . . . . . . 0.556

Franklin County, Mississippi. . . . . . . . . . . . . . 0.555

Manassas Park city, Virginia. . . . . . . . . . . . . . 0.339

Blaine County, Nebraska. . . . . . . . . . . . . . . . . 0.337

Kendall County, Illinois. . . . . . . . . . . . . . . . . . . 0.332

Craig County, Virginia. . . . . . . . . . . . . . . . . . . 0.327

Bath County, Virginia. . . . . . . . . . . . . . . . . . . . 0.326

Logan County, Nebraska. . . . . . . . . . . . . . . . . 0.314

San Juan County, Colorado. . . . . . . . . . . . . . . 0.313

McPherson County, Nebraska. . . . . . . . . . . . . 0.311

Kalawao County, Hawaii. . . . . . . . . . . . . . . . . 0.304

Loving County, Texas. . . . . . . . . . . . . . . . . . . . 0.207

Source: U.S. Census Bureau, 2006–2010 American Community Survey. 
U.S. Census Bureau 5

WHAT IS THE AMERICAN 

COMMUNITY SURVEY?

The American Community Survey (ACS) is a nationwide survey 

designed to provide communities 

with reliable and timely demographic, social, economic, and 

housing data for the nation, states, 

congressional districts, counties, 

places, and other localities every 

year. It has an annual sample size 

of about 3 million addresses across 

the United States and Puerto Rico 

and includes both housing units 

and group quarters (e.g., nursing 

facilities and prisons). The ACS is 

conducted in every county throughout the nation, and every municipio 

in Puerto Rico, where it is called 

the Puerto Rico Community Survey. 

Beginning in 2006, ACS data for 

2005 were released for geographic 

areas with populations of 65,000 

and greater. For information on the 

ACS sample design and other topics, visit <www.census.gov/acs

/www>.