The striker, making his first appearance since signing on a month's loan from Scunthorpe, scored three times in 21 minutes to leave Barnet boss Paul Fairclough shell-shocked.
Richard Butcher's spectacular left-foot volley gave the visitors the lead after just seven minutes, before Forte stole the show with a devastating show of finishing.
Barnet improved in the second-half with Albert Adomah going close with a rasping effort, but by then, the visitors were home and dry.
The hosts had started brightly but their failure to make their early dominance count cost them dear as County took the lead with their first real opportunity of the game.
It was Forte who created the chance, flicking the ball into the path of Butcher, who flashed a first-time volley past the outstretched arm of Harrison in impressive fashion.
That goal stunned the home side and their spirits were further knocked just seven minutes later, as Forte took advantage of some dreadful defending before slamming home Jamie Clapham's cross from close range.
Barnet rallied briefly with Neal Bishop firing inches over the crossbar, but the home side's failure to defend saw County further extend their lead as Forte capitalised on yet another mistake.
The former Doncaster man beat Ismail Yakubu to the ball and sent a crashing effort past the exposed Harrison from 12 yards to send County into dreamland.
County had not tasted victory in their past six league games before their arrival at Underhill, but they looked in the mood to run up a cricket score in north London with Barnet firmly on the ropes.
And Forte delivered the knockout blow right on half-time, racing through on goal before lifting the ball over Harrison and slotting the ball into the empty net.
Fairclough made a change at the break, introducing Nicky Deverdics in place of the woeful Max Porter, but it made little difference with Barnet so far adrift.
Adomah and O'Flynn briefly threatened with County having taken their foot off the pedal, but the game was already up as the Bees slumped to an embarrassing defeat.