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 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).

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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>.
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.