N.H. Rev. Stat. Ann. § 510:10

Service of writs against counties may be made upon one of the county commissioners and the treasurer for the county; against cities, upon the mayor or one of the aldermen and the city clerk, or in a city where the city manager is chief administrative officer and the head of the administrative branch of the city government, upon the city manager and the city clerk; against towns, upon one of the selectmen and the town clerk; against school districts, upon one of the members of the school board and the clerk of the district; and against village districts, upon one of the commissioners and the clerk of the district.