N.J. Stat. § 44:1-62
A municipality may subsequently join in such county or joint county purpose by ordinance which shall be adopted by referendum in the manner provided by sections 40:49-9 to 40:49-12 of the title Municipalities and Counties. After the adoption of the ordinance, the notification of the board of chosen freeholders, and the acceptance and approval of the ordinance by the board of freeholders by resolution after notice of the time and place of the consideration thereof is given to the public who shall be afforded an opportunity to be heard thereon, the municipality shall thereafter have like responsibilities in respect to the purpose as though it had originally participated therein, and shall assume such share of the cost of buildings and equipment theretofore constructed and installed as shall be prescribed by the board of freeholders.
N.J.S. § 44:1-62