N.J. Stat. § 54:4-4: Certain municipal land extending into another county

Where land belonging to one municipality and used for public purposes extends into an adjoining municipality, and, by reason of the forming of a new county or the annexation of territory from one county to another, a portion thereof is thereby located in a different county from that in which the municipality owning it is located, the land and all improvements thereon shall be exempt from taxation, but the area of the land extending into the adjoining municipality in another county shall not exceed five acres.