Republican state Rep. Jason Perillo, from Shelton, has defeated Democrat Tony Afriyie from Stratford for the 21st District state Senate seat.
The district covers Monroe, Seymour, Shelton and Stratford.
The special election on Tuesday filled the vacancy created when former state Sen. Kevin Kelly resigned in January after being nominated as a Superior Court judge.
With Perillo's winning of the Senate seat, his House seat in the 113th District will need to be filled in another special election.