Done has now scored four goals in just three Blades appearances since joining the club from Rochdale on deadline day.
The Blades were terrific in the opening half-hour at Meadow Lane.
They deservedly went ahead after 16 minutes when the Magpies were caught napping from a throw-in.
Rob Harris was alert as he took it quickly, and he found Jamie Murphy who lashed a shot superbly beyond veteran goalkeeper Roy Carroll to register his ninth goal of the season.
Nigel Clough’s men then went close twice inside the following five minutes to doubling their advantage.
Done appeared determined to continue his blistering start for his new club.
However, he volleyed narrowly wide, and Jason Holt then turned neatly before shooting and forcing Carroll into a smart block. Harris was then unfortunate as he saw a shot saved after his initial free-kick was blocked by the Magpies’ wall.
The Blades fans were screaming for a penalty in the 32nd minute when it appeared that midfielder Louis Reed was pulled back in the box, but this time the referee was unmoved.
As if to rub salt in that wound, the hosts went on to equalise three minutes later.
A deflected cross came in from Will Hayhurst, but Liam Noble adjusted superbly to back-heel a cheeky effort past Iain Turner from close range.
Reinvigorated thanks to their goal, the Magpies bossed the third quarter of the game.
Hungarian loan striker Balint Bajner twice went close, and Curtis Thompson forced Turner into a fine stop.
However, it was Done who was to clinch another crucial Blades victory with 15 minutes to go when he poked home from close range after a cross into the danger zone by Harris.
United are 11 points off second-placed MK Dons.
Notts County: Carroll, Dumbuya, Mullins, Edwards, Adams, C Thompson, Jones (Woolery 78), Noble, Hayhurst (Newton 78), Bajner, G Thompson. Unused substitutes: Pilkington, Hollis, White, Daniels, Harrad.
Sheffield United: Turner, Brayford, Basham, Kennedy, Harris, Reed (McNulty 63), Coutts, Doyle, Holt (Alcock 86), Done (Freeman 88), Murphy. Unused substitutes: Willis, Davies, Campbell-Ryce, Adams.
Referee: D Bond (Lancs).