HARRISBURG — An Allegheny County ordinance that barred registered sex offenders from living in certain areas is invalid, Pennsylvania’s highest court has declared, saying it is pre-empted by state laws that balance public safety and the goal of rehabilitation for offenders.

The prohibition against registered offenders living within 2,500 feet of schools, child-care facilities, community centers, public parks or recreational facilities would isolate many in what would amount to “localized penal colonies” distant from families and old neighborhoods, Supreme Court Chief Justice Ronald Castille wrote in a 23-page decision released Thursday.

“The county’s legislative effort in this instance undermines the General Assembly’s policies of rehabilitation, reintegration, and diversion from prison of appropriate offenders and significantly interferes with the operation of the sentencing and parole codes,” Castille wrote in a unanimous opinion.

In addition to Allegheny County, the decision affects many of the roughly 150 local ordinances around the state that are similarly designed to prevent offenders from moving to certain areas, although lawyers expressed different opinions about the impact.

The ruling effectively invalidates all the local ordinances, said Edwin J. Strassburger, who worked with lawyers from the American Civil Liberties Union of Pennsylvania in representing six sex offenders affected by the ordinance who sued in federal court in Pittsburgh.

But Allegheny County Solicitor Michael Wojcik, who led the county’s legal team, suggested that local ordinances that are less stringent or that cover more rural areas might survive.

“It does not strike them all down,” he said. “We’re a very urban county.”