I'm in Middlesex county but I heard it was not allowed in Union county. Although I have done a little bit of detecting there with no problems. I usually stay off the beaten path so I would not expect anyone to say anything since it would require them to hike through the woods to get to me. My policy is that I'll detect until I'm asked not to, then I will leave right away. If there are any signs saying that detecting is not allowed I would never try to do it and always stay away from national parks / monuments / historical sites.
I've only had one time where an older man asked me to stop detecting a local school. I just found a nice Barber dime and he was right behind me. I tried to talk to him and show him that I leave virtually no sign that I was there but he did not want to hear it. He was also complaining that the local kids play football there and it rips up the grass. I said I was sorry and left. Knowing it is allowed in my town I just came back another day...It is just not worth an argument that nobody will win. Plus I didn't know who the man was so maybe he has some pull in town and could get metal detecting banned...you just don't know and I'm not done with the schools and parks yet. LOL
NJ