A header from Millwall's Ylenia Priest in the first half was cancelled out by Jones firing home the equaliser just ten minutes after the break.
And despite plenty of pressure, the visiting Blades couldn't find a winner.
Carla Ward's side should have been ahead after just six minutes when Riva Casley's slip gave Tania Marsden a clear sight of goal but the striker fired wide, one of several chances wasted that United would go on to rue.
Looking a fourth win in five, the Blades continued to press but couldn't find a way through a resolute Millwall defence and the hosts took the lead shortly before half-time.
Priest's excellent header from a corner put the hosts into the lead and it was an advantage they should have doubled when Evie Clarke's touch let her down in front of goal just minutes later.
Izzy Ford saw an effort deflected just wide right before half-time but United did find a response ten minutes into the second half.
Ford's cross from the right was hooked back across goal by Veatriki Sarri and Jones fired home from close range after her initial header had been saved.
The goal came just after Millwall felt they should have had a penalty for a foul on Clarke but the rest of the game largely saw the hosts defending an onslaught of United pressure.
Substitute Chloe Dixon saw several efforts blocked, as did Sam Tierney, as the visitors pushed and pushed for a winner that never came.
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