First-half goals from David Raven and Billy McKay put Caley Thistle firmly in control, and they held firm after the break before substitute Marley Watkins made sure of the three points.
The visitors took only eight minutes to break the deadlock when Evangelos Ikonomou drove in a low cross for Raven to steer confidently past Mark Brown.
Jamie Vincent, who replaced Watkins in Thistle’s starting line-up, sliced wide from Richie Foran’s clever cut-back with County’s defence struggling to keep up.
County finally roused the home faithful when Richie Brittain’s decent long-range effort warmed the palms of Dean Brill.
But back came Inverness as Aaron Doran’s inviting cross narrowly evaded everyone in the box, and Doran himself then drilled a fierce shot inches wide of the target.
But Caley Thistle doubled their lead five minutes before half-time when Billy McKay collected Graeme Shinnie’s pass on the edge of the box and gave Brown no chance with a precise finish.
The home side improved after the break and Michael Tidser’s snapshot forced a smart reaction save from Brill, who then got his angles right to keep out a firm drive from Yoann Arquin.
The Inverness goalkeeper was again well placed to deal with a Yann Songo’o header before Greg Tansey lashed over the bar at the other end following a flowing counter-attack.
Brill kept out a neat turn and shot from Jordan Slew, and a shot from Filip Kiss beat the visiting keeper but shaved the outside of the post.
But Thistle effectively put the result beyond doubt on 78 minutes when Ross Draper’s defence-splitting pass found Watkins, who rolled a composed finish past Brown and in off the upright.
A thunderbolt from Shinnie just cleared the bar in the late stages as Inverness ran out comfortable winners and moved within three points of third-placed Motherwell.