The population of the United States grew at its slowest pace in more than eight decades, the Census Bureau said Wednesday, as the number of deaths increased and the number of births declined.

Not since 1937, when the country was in the grips of the Great Depression and birthrates were down substantially, has it grown so slowly, with just a 0.62 percent gain between July 2017 and July 2018. With Americans getting older, fewer babies are being born and more people are dying, demographers said.

The past year saw a particularly high number of deaths — 2.81 million — and relatively few births, 3.86 million. If the pattern continues, immigrants will soon be more important to population gains than the so-called natural increase, which is the number of births minus the number of deaths. That was not the case 10 years ago, when natural increase accounted for a far higher share of the country’s population gains.

“The aging population is starting to take its toll,” said William Frey, a demographer at the Brookings Institution. “I think we need to get used to the fact that we are now a slow-growth country.”