Could it be that, at some time in the past, "Pompton Plains" was a New York postal zone whose service area included part of adjoining New Jersey? A mailing address can be quite confusing as to where exactly -- in which community -- a place is located. The last line of any place's mailing address, anywhere in the U.S., is: Postal City, Postal State & ZIP Code There are numerous places where the postal zone is based in a different state than is the community being served. For example: Fisher Island, and island hamlet in the Town of Southold on Long Island's north fork, has a Connecticut '06' ZIP code as its mail is delivered out of New London, CT. Parts of western Massachusetts have a New York ZIP Code as their mail is delivered out of a postal in New York State. I hope this information is useful or, at least, interesting. Regards, Walter Greenspan Great Falls, MT & Jericho, NY