Ivan Sproule scored the only goal of the game in the 11th minute with a superb strike from the edge of the 18-yard box.
Saints dominated for long spells after the break but they found man-of-the match Mark Brown in outstanding form.
Saints started on the front foot and Mehdi Abeid tested Brown with a low drive in the seventh minute but the County keeper made a comfortable save.
But it was County who took the lead four minutes later when Michael Kovacevic and Sam Morrow linked and when the ball broke to Sproule he curled the ball into the far corner of the net for the opener - his fourth goal in as many starts.
It was an open game and Saints looked dangerous going forward and were far from out of it.
Steven Maclean looked as if he was sure to grab an equaliser in the 16th minute when he beat his marker and fired a shot towards the far corner and it took a brilliant one-handed save from Brown to deflect it behind for a corner.
Abeid flashed another shot over as Saints kept the pressure on.
Then Liam Craig cut inside Kovacevic on the left hand side of the box but his shot was parried by Brown at the near post.
There was little in the way of goalmouth incidents before the break with play getting bogged down in the middle of the park.
The visitors made a promising start to the second half and it took a timely intervention from Grant Munro to stop Rowan Vine in his tracks after the Saints forward played a one-two with Abeid.
It was non-stop pressure on the County goal and Brown did well to save with his legs from Craig in a crowded goalmouth in the 55th minute.
The County goal got a reprieve four minutes later when they broke up the left and after Paul Lawson and Rocco Quinn linked-up Sproule cut inside, but his shot was well saved by Allan Mannus.
In another breakaway move in the 64th minute Sproule sent a dangerous ball into the Saints box but it was just too high for Morrow who had the goal in his sights.
Richard Brittain had the chance to make an impact against his future employers with a free kick in the 77th minute, but his effort flew a yard wide of Mannus' right-hand post.
Then Lawson let rip with one of his long-range attempts which flashed over the crossbar.
Craig fired a shot wide of target in the third minute of injury time but County held out for a hard-earned three points.