If you want to count these as parks:
Playland Castaway Cove, Ocean City, NJ-20 minute walk
Gillian's Wonderland, Ocean City-2 miles ?
Morey's Piers, Wildwood, NJ, <30 miles
For real theme parks:
Six Flags Great Adventure-about 70 miles
Dorney Park
Hershey Park
Clementon Park is closer, but I haven't been there in over 10 years.
(I moved from Long Beach Island to Ocean City, NJ in 2014. Maybe I should change my user name.)