Cook County Comms. Bridget Gainer (D-10) and Frank Aguilar (D-16) both lost their bids for reelection Tuesday against primary challengers. [Provided]

With four open races and the defeat of two incumbents Tuesday, the 17-member Cook County Board of Commissioners will have at least six new members next term, according to unofficial election results from the Cook County Clerk's Office and Chicago Board of Elections.