Racial segregation in U.S. neighborhoods has declined over the past several decades but it remains very high. Meanwhile, residential segregation by income has risen sharply from the relatively low levels in the 1970s. Large metropolitan areas are among the nation’s most segregated regions, and while none are meaningfully integrated, some are divided far more along racial lines than others.

To identify the most segregated neighborhoods in America, 24/7 Wall St. constructed an index based on the share of a metro area’s population living in racially homogeneous zip codes — areas where more than 80% of the population is of a single race or ethnicity. In metro areas with complete integration, every zip code has the same racial/ethnic distribution as the area’s whole population. In areas with the worst segregation, no one lives in a zip code with anyone of a different race/ethnicity.

We reviewed only metropolitan areas with more than 1 million residents. Of those, since racial segregation is only possible in areas with people of various ethnicity, only 29 sufficiently diverse metropolitan areas were considered. Based on our index, more than a third of residents in nine U.S. metro areas live in homogeneous zip codes, segregated from other racial groups.

According to Richard Rothstein, research associate at the Economic Policy Institute (EPI), segregation is no accident. Federal housing policies starting in the 1930s are largely to blame for ongoing racial segregation and its economic effects. For example, in the last 60 years, black families were intentionally excluded from affordable housing options across the nation’s growing suburban neighborhoods. As a result, the predominantly black zip codes in America’s most segregated metro areas tend to be located near the city centers, while the predominantly white zip codes are more often found outside the city, in the suburbs.

6. Nashville-Davidson–Murfreesboro–Franklin, TN

> Pct. of population living in segregated areas: 45.0%
> Black poverty rate: 25.2%
> White poverty rate: 10.5%
> Black unemployment rate: 11.1%
> White unemployment rate: 4.7%

The gap between white and black median household incomes in the Nashville area is $21,034, making Nashville one of only three metro areas reviewed with a lower gap than the national one.Nashville However, while the white unemployment rate of 4.7% was well below the national jobless rate, 11.1% of black area workers were unemployed. And while just over one in 10 white residents lived in poverty, more than one in four black residents did.

Also, like in nearly every other U.S. metro area, the poorest zip code in the Nashville area is predominantly black. The 37208 zip code is located near downtown Nashville, while the predominantly white neighborhoods are largely located outside the city proper. As is the case in most of the country, residential segregation in the Nashville area is largely due to federal home-financing policies in the 1950s that were unavailable to black residents. As Rothstein explained, the intentional segregation of these neighborhoods also contributed to income and wealth disparities.

For black area residents, less than 40% of housing units in five of the nine segregated cities were owned by their occupants. In contrast, homeownership rates among whites exceeded 70% in all but one of the nine cities.

Since wealth largely comes from housing investments, and home values have increased dramatically over the decades in many areas, those policies have exacerbated income and wealth disparities, Rothstein explained. Black Americans earn about 60% of what white Americans do, and accumulated wealth among typical black households is a mere 6% of the typical white household.

Those federal segregation policies, and the resulting economic fallout for black Americans, have contributed to lower educational attainment rates in segregated schools. Commenting on the effects of racial segregation in the school system, Rothstein said, “When you concentrate children with disadvantages in the same classrooms, the whole of instruction becomes remedial and below grade level.”

Racial and socioeconomic segregation are closely linked, especially in large U.S. metropolitan areas. The predominantly nonwhite neighborhoods in all but one of the nine most segregated metro areas have significantly lower educational attainment rates than those of white neighborhoods and the national rates. Segregation along racial lines is also associated with income segregation. The difference between black and white median household incomes exceeded the national gap of $22,681 in all but three of the 29 metro areas reviewed.

Segregation is in many ways a black/white phenomenon, although Hispanics and Latinos also frequently live in segregated neighborhoods. The Boston metro area is the only region considered where segregation impacted the Hispanic population more than blacks. Rothstein said, “For African Americans, it was the product of explicit public policy to segregate them from the rest of society. For Hispanics, it’s the result of traditional patterns of ethnic immigration.”

For Rothstein, racial and socioeconomic segregation must be undone in the same way it was implemented — by a federal desegregation policy. While federal policies make up the bulk of the explanation, the reasons for segregation persisting today are perhaps more complicated. In a recent report from researchers at Stanford University, “Neighborhood Income Composition by Household Race and Income, 1990-2009,” the authors observe that “Other factors, such as differences in household structure, lingering racial discrimination in the housing market, the location of affordable and subsidized housing, and residential preferences, likely also play a role.”

Click here to see America’s most segregated cities.

Click here to see our full methodology