Tri-County scored twice in the second quarter to take a 12-7 lead into the half.
The Packers, who have not won in 26 straight games dating back to October 2014, took a lead when Koomen connected on a 39-yard touchdown pass to Riley Krim in the thrid quarter. Koomen added a two-point conversion run with 46 seconds to play in the quarter for a 15-12 lead.
Tanner Ching scored from a yard out for his third and final rushing touchdown of the night, giving Tri-County a 20-15 lead with 10:22 to play in the final quarter.
Fremont was led by Krim who had three catches for 71 yards, and the running back duo of Parker Dalson and Kane Widing, which combined for 160 yards on 39 carries.
Fremont falls to 0-8 on the season and finishes the season against McBain next Friday.