The Dingwall side had not beaten United since 1998 when their now manager Derek Adams scored both goals in a 2-0 victory in a League Cup clash.
Although United had to play the last half an hour with 10 men after Barry Douglas was sent off, County fully deserved their victory.
Sproule notched the only goal of the game in the 64th minute when he nodded in an Iain Vigurs cross.
County midfielder Vigurs had the first shot on target in the third minute, but United goalkeeper Radoslaw Cierzniak made the save.
Vigurs had another chance to hit the target a minute later, but when the ball fell for him 10 yards out he mis-hit his shot.
The home side were enjoying most of the possession and Sproule tried to get on the end of a defence-splitting pass from Paul Lawson, but Cierzniak raced from his goal to clear the danger.
United's first chance arrived in the 15th minute when Jon Daly rose to meet Stuart Armstrong's cross on the six-yard line, but his header flew wide.
John Souttar found himself in referee Kevin Clancy's book four minutes later after he stuck out an arm to stop the ball reaching Steffen Wohlfarth.
Although County were on top it was United who almost snatched the lead on the half-hour mark when Daly stooped to get his head to a Douglas free-kick, but Michael Fraser dived at full stretch to make a brilliant save.
The second half started brightly with both teams showing their intent in going forward.
The first chance came County's way when Mihael Kovacevic got behind the United defence, but his cut-back was fired wildly over the away stand.
But County made the breakthrough in the 53rd minute when Lawson picked out Vigurs, who got to the byline and his cut-back was nodded in at the back post by Sproule.
It got worse for the Tangerines 11 minutes later when Douglas lunged in on Sproule and the referee immediately showed a red card.
County were turning on the style and the United goal survived in the 77th minute when Richard Brittain rattled a shot off the top of the crossbar.
Brittain was involved again in the 84th minute when he scooped a Vigurs delivery past the wrong side of the upright.
- Sports & Recreation
- Iain Vigurs