There are many campgrounds along Rt 9 south of Atlantic City. If you want to go to traditional boardwalk type of town, then you might want to go to Ocean City. Whipporwill campgrounds would be closest to this point. Stayed there many times. Nice, big sites.
If you want to go further South towards Sea Isle or Avalon, then Avalon campground would be my recommendation. Small cute park.
Next point going South would be Stone Harbor and Wildwood. Seashore campsites and Big timberlake campground are nice parks near this area.
Furthest point South is of course Cape May. Beachcomber, Holly Lakes are both nice campgrounds in this area.
We have stayed in all these campgrounds. All are nice. Just depends which part of the Jersey shore you want to go to.