How "post-racial" is America? Not very, according to an ongoing Reuters poll, which shows that nearly 40 percent of white Americans are surrounded exclusively by friends who are also white Americans.

Accounting for coworkers along with friends and relatives, the poll found that 30 percent of Americans overall aren't mixing with people of other races.

That could partly explain the racial divide on issues like the George Zimmerman trial. After he was found not guilty of murdering unarmed teenager Trayvon Martin, a Pew Research Center poll found that 86 percent of African-Americans expressed dissatisfaction with the verdict, compared to just 30 percent of whites.

The same poll found that 78 percent of blacks said that the case should spur a conversation about race. Only 28 percent of whites agreed, with 60 percent of them saying that the issue of race was getting too much attention.

A recent study by the American Sociological Review found that while America's neighborhoods are more diverse than ever, most of the people moving to those diverse neighborhoods haven't been white and black families. The Reuters poll backed that finding, noting that Latinos were the most likely to have friends and marry outside of their own race.

"There has been some progress, but whites and blacks in particular still tend to live in separate neighborhoods," Camille Zubrinsky Charles, a professor of sociology at the University of Pennsylvania, told NBC News.

While American might look like a divided country now, the poll did contain hopeful signs for the future.

Only 10 percent of Americans under 30 years old reported having no friends, coworkers, or family outside of their race — half the rate for the country as a whole.