New York City ? The number of U.S. children in foster care has dropped 8 percent in just one year, and more than 20 percent in the past decade, according to new federal figures underscoring the impact of widespread reforms.

The drop, hailed by child-welfare advocates, is due largely to a shift in the policies and practices of state and county child welfare agencies. Many have been shortening stays in foster care, speeding up adoptions and expanding preventive support for troubled families so more children avoid being removed from their homes in the first place.

The new figures, released Tuesday by the Department of Health and Human Services, show there were 423,773 children in foster care as of Sept. 30. That’s down from 460,416 a year earlier and from more than 540,000 a decade ago.

California had the biggest one-year drop — from 67,703 to 60,198. Just eight years ago, the state had more than 90,000 children in foster care.

Florida, Illinois, New York, Ohio and Pennsylvania are among other major states that have lowered their numbers sharply over the decade.