Schalk scored the only goal of the game in the 14th minute when he drilled the ball into the far corner of the net from the edge of the 18-yard box.
Thistle dominated the second half but County withstood the onslaught, and with other results going their way they booked a place in the top six of the Ladbrokes Premiership.
There was little in the way of goalmouth action in the early stages, but the game came to life with the first shot on target, which also produced the opening goal.
Schalk picked up the ball on the edge of the area and after taking a touch he fired a low shot past Ryan Scully in the Partick net.
Partick tried to respond but they should have been 2-0 down in the 24th minute when Schalk hit the bye-line before cutting the ball back to Brian Graham 12 yards out. However, his shot was well blocked by Gary Miller and Partick survived.
It could easily have been 1-1 soon after that only for Scott Fox, back in the County goal after six weeks, pulled off a fantastic save from Ryan Edwards who let fly from 25 yards.
It was end to end stuff and Schalk, who was looking in the mood, fired just wide of the far post with a fierce drive.
But the visitors continued to threaten and Mathias Pogba hooked a ball over the crossbar from near the penalty spot.
Thistle created a chance in the first minute of the second half when a cross from Abdul Osman was flicked towards goal at the near post by Pogba but Fox was alert enough to turn the ball behind for a corner.
Then a dangerous cross from Callum Booth was met by Edwards on the six-yard line but his header went wide.
Thistle kept searching for an equaliser and Booth was almost in only for Fox to race from his goal and smother the ball.
It was practically one-way traffic and County were only seen as an attacking force in snatches.
Michael Gardyne made room for a shot with four minutes remaining but his effort was easily saved by Scully.
At the other end Thistle substitute Kris Doolan flashed a shot past Fox’s left-hand post as the visitors finished strongly.
But despite all the pressure County held out until the final whistle.