The state is closing California's largest youth prison as the population of juvenile delinquents in state custody continues to decline, corrections officials announced today.

The facility, the Heman G. Stark Youth Correctional Facility in Chino, will be converted into an adult prison.

Officials said the move is part of a plan to "right-size" staff at the Department of Juvenile Justice, which is downsizing its workforce by 400 employees this year in an effort to save the state up to $40 million.

The plan also is geared toward reducing treatment costs for youth inmates from $252,000 per person to $175,000, state officials said.

The Chino facility opened in 1959 and now houses less than 400 juvenile inmates. They will be redirected to other facilities. An exact date by which the closure will be completed has not yet been determined.

The number of juvenile offenders in state custody has dropped over the last 10 years from a peak of nearly 10,000 to approximately 1,700, the result of legislation that now puts most young inmates in county jails.