Such is the case in Ferguson. The part where Mr. Brown died is a predominantly black east side neighborhood where residents have complained of police harassment and high crime in a cluster of apartments that stretches into the census tract with the most Section 8 renters in Missouri. Life is much different just two miles away in the city’s amenity-filled central business district, surrounded by pockets of predominantly white, affluent neighborhoods with sturdy brick and clapboard homes.

Responding to concerns that the conditions in black, lower-income neighborhoods contributed to the problems that sparked the unrest after Mr. Brown’s death, the Ferguson Commission, convened by Gov. Jay Nixon, recently proposed measures to promote more integrated housing, including vigorously enforcing fair housing laws to reduce discriminatory lending practices.

Interviews with residents, activists and academics suggest that an array of forces perpetuating segregation remain very much a thing of the present. In some ways, they are fueled by the attitudes of people, both black and white, molded over generations. In other ways, they are an economic reality that is fortified by real estate practices and government policies.

Over the years, the federal government has regularly failed to enforce fair housing laws that could reduce segregation. The Obama administration last month introduced new regulations through the Department of Housing and Urban Development that are intended to get localities to work more vigorously toward breaking down racially divided housing patterns.

The Section 8 voucher program, started four decades ago, is one of the tools that federal officials had hoped would provide access to high-opportunity communities for low-income people — and, by extension, minorities, as two out of three voucher recipients nationwide are not white.

In practice, however, the voucher system often falls short of that goal.

When she began her housing search shortly after receiving her letter, Ms. Wade plugged her wish list into the websites on which many landlords who accept Section 8 vouchers advertise — a two-bedroom house with a landlord who did not require two months’ rent upfront, something she could not afford. When the hits came back, not a single property was in one of the more affluent towns where the schools are better and crime lower. The few that were near promising areas had monthslong wait lists. Some landlords told her that they would rent to her and the children, but not to her boyfriend.