WASHINGTON — The percentage of the nation’s black population living in the South has hit its highest point in half a century, according to census data released Thursday, as younger and more educated black residents move out of declining cities in the Northeast and Midwest in search of better opportunities.

The share of black population growth that has occurred in the South over the past decade — the highest since 1910, before the Great Migration of blacks to the North — has upended some long-held assumptions.

Both Michigan and Illinois, whose cities have rich black cultural traditions, showed an overall loss of blacks for the first time, said William Frey, the chief demographer at the Brookings Institution.

And Atlanta, for the first time, has replaced Chicago as the metro area with the largest number of African-Americans after New York. About 17 percent of blacks who moved to the South in the past decade left New York State, far more than from any other state, the census data show.