If it is illegal I was not aware of it . I know here on Long Island a permit is required to MD on NYS parkland's and it cost's $40 and is valid 4/1 to 3/31 of the following year . But when I looked into upstate NY I did not see anything about it being illegal . There are some parks upstate that a permit is required and from what I have read it cost's $20 (one that I can think of off the top of my head is Harriman SP) . There is a lot of NYS land that is not considered a "park" where snowmobiling , horseback riding etc is allowed so I can't see NYS just not allowing metal detecting . I don't know the laws regarding Greene County and local municipalities land . I guess some research is in order .