The decision by the 4th District Court of Appeal found the state already had a "comprehensive statutory scheme regulating the daily life of sex offenders," the Los Angeles Times reported Friday.
The decision overturns the conviction of Hugo Godinez, a registered sex offender, in Orange County of a misdemeanor for attending a company picnic at a public park in Fountain Valley in 2011.
He was convicted of sexual battery in 2010.
The Orange County ordinance allows sex offenders to go to public parks with written permission of the sheriff. The court said such a requirement amounted to a "de facto registration requirement" that ran counter to state law.
The Orange County District Attorney's office will decide next week whether to appeal the ruling, said Susan Kang Schroeder, the office's chief of staff.