The United States population grew only 0.72 percent last year, to 316,128,839 in July from 313,873,685 a year earlier, according to figures released Monday by the Census Bureau.

It was the lowest rate in more than seven decades, said William Frey, a demographer at the Brookings Institution in Washington.

“The census projections to 2060 have us going down to half a percent because we’re an older population, and aging populations don’t grow so much,” Mr. Frey said. “If we have very sharp declines in growth, that takes a bite out of the economy.”

For the time being, New York remains the nation’s third most populous state, after California and Texas — but its lead over Florida narrowed to fewer than 100,000 people over the last year, according to the census figures. If New York’s tepid growth rate and Florida’s rapid one continue over the next year, Florida will pull ahead.