DETROIT—The population of Detroit has fallen back 100 years.

The flight of middle-class African-Americans to the suburbs fueled an exodus that cut Detroit's population 25% in the past decade to 713,777, according to Census Bureau data released Tuesday. That's the city's lowest population level since the 1910 census, when automobile mass production was making Detroit Detroit.

The decline, the fastest in city history, shocked local officials, who had expected a number closer to 800,000. Mayor Dave Bing said the city would seek a recount.

"If we could go out and identify another 40,000 people that were missed, and it brings us over the threshold of 750,000, that would make a difference from what we can get from the federal and state government," Mr. Bing said at a news conference Tuesday.

In all, the city lost more than 237,000 residents, including 185,000 blacks and about 41,000 whites. The Hispanic population ticked up by 1,500. Meanwhile, the black population in neighboring Macomb County more than tripled to 72,723, constituting 8.6% of the county's population in 2010, compared with 2.7% a decade earlier. Oakland County's African-American population rose 36% to 164,078.