The best chances of a tentative first half fell to County, with an Alan Judge cross-shot just being diverted towards the net by Yoann Arquin, only for Matt Duke to somehow keep it out.
Duke was at full stretch again moments later when Alan Sheehan's left-foot drive was foiled before the County left-back planted the follow-up inches over the bar.
In injury time, following a poor second half, Lee Hughes' shot was parried by Duke and Arquin incredibly hit the rebound on to the bar from three yards out.
The home side were made to pay in extra time as poor defending by the Magpies on the edge of their own box saw the ball fall to Hanson, who curled into the top corner.
