Richard Brittain headed in the winner after 57 minutes as the visitors won for the first time in almost two months to emulate Aberdeen and claim a second win over Hibs from two attempts this season.
The start was disjointed as possession was frequently relinquished, with Tim Clancy's blast into the second tier of the stand barely deserving of being called a shot.
Hibs were beginning to get a foothold in the game, but County were resilient.
An insipid first half closed after Paul Cairney shot well wide as a free-kick from a promising position was played short to him.
The second period was offering much of the same uneventful fare as the first until Hibs hesitated, allowing Iain Vigurs time and space in the left channel to loft a ball forwards.
The ball looped towards Brittain 15 yards out and his header beat Ben Williams and flew into the top corner. It was the midfielder's fifth of the season.
Mihael Kovacevic, Vigurs and Clancy, who ran 40 metres to remonstrate with the official, all saw yellow before McPake was booked for a sliding challenge when he appeared to win the ball.
The time was ticking for Hibs and little more than 20 minutes remained when football matters resumed.
A Ryan McGivern cross from the left was headed over by Eoin Doyle before substitute Jorge Claros, on for Tom Taiwo, had a shot turned around the post for a corner by Mark Brown.
Doyle had the ball in the net 16 minutes from time, but he was flagged offside in reacting first to a Brown save from Leigh Griffiths' shot.
The left flank was proving a useful source of supply for Hibs and McGivern's accurate cross was met by Griffiths, who should have done better than head straight at Brown from six yards out.
With four minutes remaining, Hibs exchanged defender Clancy for striker Shefki Kuqi in an effort to find an equaliser, but, it did not materialise as the visitors emulated the Dons and Motherwell in claiming victory in Leith this term.