N.J. Stat. § 40:20-20
The board of chosen freeholders in each county shall consist of that number of members authorized for the county immediately prior to the effective date of this 1981 amendatory act. At any time after that date, a proposition may be submitted to the voters of the county to increase or decrease the number of members of the board of chosen freeholders to three, five, seven or nine. The proposition shall be submitted either upon adoption of a resolution by the county governing body after a public hearing thereon, or upon submission to the county clerk of a petition signed by a number of the legal voters of the county equal in number to at least 15% of the total votes cast in the county at the last election at which members of the General Assembly were elected. The proposition shall not be submitted more than once in any 3 year period.
A petition submitted pursuant to this section shall be verified, inspected and certified as to the authenticity of the signatures attached thereto by the county clerk within 20 days of submission, and shall be submitted at the next general election occurring at least 40 days after certification.
The question of the increase or decrease in the number of members of the board of chosen freeholders shall be submitted to the voters at the election in substantially the following form:
"Shall the membership of the board of chosen freeholders of be from (insert name of county) (insert "increased" or "decreased" as appropriate) to members?" (insert current number) (insert proposed number)
A canvass and return of the vote upon the proposition shall be made by the election officers in the same manner as for officers voted for at the election, and a majority of all the votes cast upon the proposition in favor of the proposition shall be sufficient to make the change.
When the voters shall have voted to increase or decrease the membership of the board of chosen freeholders as provided in this section, the increase or decrease shall take effect for the next general election of chosen freeholders.
Nothing in this section shall apply to any county that has adopted a charter pursuant to the "Optional County Charter Law," P.L. 1972, c. 154 (C. 40:41A-1 et seq.).
N.J.S. § 40:20-20