N.J. Stat. Ann. § 19:6-23

Each member of the county board shall, before entering upon the performance of his duties, take and subscribe an oath or affirmation, in writing, before the clerk of the county for which he is appointed, faithfully and impartially to discharge all his duties as such officer, to the best of his skill and ability. Such oath or affirmation shall be forthwith recorded in the office of the county clerk, and after so qualifying any member of such board may at any meeting thereof administer any oath or affirmation required or permitted to be taken by this title.