West Chicago resident Al Murphy defeated three other Republicans vying for their party's nomination for the District 6 seat on the DuPage County Forest Preserve Commission.
Republican incumbent Roger Kotecki, who has held the seat for 20 years, is stepping down after the general election.
With all 110 precincts reporting, Murphy had roughly 40 percent of votes, Peter Connolly of Wayne had nearly 30 percent, Kory Atkinson of Roselle had about 16 percent and Arthur Pierscionek of Bartlett had about 14 percent.
Murphy will face Democrat Shannon Burns in November, who ran unopposed in Tuesday's primary. The winner's term will either be 2 or 4 years. The length will be determined by lottery after the November election, in which all seats are open.
District 6 includes all or parts of Warrenville, Batavia, West Chicago, Wheaton, Winfield, Carol Stream, Bloomingdale, Hanover Park, Bartlett, Wayne and St. Charles.