Paul Heffernan scored twice on his first start of the season following a dislocated shoulder and a goal from Gary Harkins ended a run of two home defeats for Killie.
The hosts were on top from the first whistle and Harkins wasted two early chances before Michael Fraser kept Kilmarnock at bay with a fine double save to keep out a Heffernan volley and Borja Perez’s follow-up.
At the other end, Stuart Kettlewell should have done better with Mark Fotheringham’s cross and Steven Ross fluffed a gilt-edged chance when teed up by Rocco Quinn eight yards out.
Fraser came to County’s rescue again just after the half-hour when he clawed the ball off the line after Michael Nelson got a touch to a Perez corner while Quinn pulled a shot wide as the visitors finished the half strongly.
Cillian Sheridan brought another fine save from Fraser after the restart with a low 20-yard shot that the goalkeeper pushed round the post.
The striker then turned provider for Heffernan and Perez in the space of two minutes but the former was denied by Fraser and the latter screwed his shot horribly wide.
But Killie’s pressure finally paid off on 68 minutes when Heffernan stooped to head home a Perez free-kick and Harkins put the result beyond doubt with a fine 18-yard drive into the top right corner on 77.
Manuel Pascali pounced on a poor clearance from Fraser but his lob drifted wide of the open goal so it was left to Heffernan to wrap it up with a thumping angled drive eight minutes from time.