The state Environmental Protection Department says visits have tripled since 1980, to a record 18.8 million people in fiscal 2010.
DEP spokesman Lawrence Hajna told The Record newspaper people are staying closer to home and taking shorter vacations.
State parks charge $5 a car on weekdays and $10 a car on weekends.
The DEP says officials have tried to maintain the same opening hours even though the number of park employees has declined 26 percent over the past decade.
Information from: The Record, http://www.northjersey.com