After dropping sharply between 2005 and 2012, the number of children in the U.S. foster care system has increased for a third year in a row, according to new federal data released Thursday. A major factor: Worsening substance abuse by parents.

The annual report from the Department of Health and Human Services tallied 427,910 children in the foster care system as of September 30, 2015, up from about 414,429 a year earlier. The peak was 524,000 children in foster care in 2002, and the number had dropped steadily to about 397,000 in 2012 before rising again.

According to the report, the foster care population rose in 2015 in nearly three quarters of the states, with the largest increases in Florida, Indiana, Georgia, Arizona and Minnesota.