Arquin was on the spot to stab the ball home in the 65th minute when the home defence had failed to clear a cross from the lively Jamal Campbell-Ryce.
It was no more than the Magpies deserved from a much-improved second-half performance and with better finishing they might have won.
Walsall began well on a heavy pitch and in the sixth minute top-scorer Will Grigg forced his way through, but saw his low shot cleared off the goalline by Alan Judge.
Grigg did collect his 11th goal of the season, however, after 29 minutes when County goalkeeper Bartosz Bialkowski flattened Jamie Paterson in a corner of the box and there was a delay while a flare thrown onto the pitch from the visitors' end was cleared.
Grigg kept his compsure to coolly send the goalkeeper the wrong way and give the Saddlers the lead they deserved.
But managerless County created more chances in the second half and were worth at least a point.