The 26-year-old Dykstra made 17 appearances for the Fire over two seasons, and posted a 5-6-6 record. He spent last season with the Charleston Battery of the USL Pro league, posting an impressive 0.98 goals-against average in 16 games.
"We are excited to have added another young goalkeeper who has a bright future in MLS," said United General Manager Dave Kasper. "Andrew has gained valuable experience in the past two years as a professional and we look forward to his contributions to our club."
Dykstra will backup No. 1 goalie Bill Hamid for United. Hamid is a member of the U.S. national team and U.S. Olympic team, and will likely miss a number of matches this season due to international duty.