The draw ended a run of three straight victories for the Owls, who missed the chance to jump to third in the table.
Preston, who also had two goals disallowed in a dominant second half, had taken the lead through a Sam Hutchinson own goal.
Callum Robinson had the first effort of the game in the 11th minute, spinning and unleashing a shot from 25 yards which was pushed around the post by Keiren Westwood.
And the hosts continued to be the better side in the opening stages, passing up another chance as Robinson picked out Simon Makienok six yards out after 22 minutes, but the Danish striker headed well wide of the near post.
When Sheffield Wednesday’s first effort of the half came after 44 minutes, it was no threat to Chris Maxwell’s goal as Ross Wallace’s 20-yard strike was high and wide.
It was Preston who began the second half on the front foot. They kept the pressure on after a corner was cleared on 51 minutes and Paul Huntington nodded down for Alex Baptiste, who fired inches wide from six yards.
Wednesday then put together their best move of the match as Barry Bannan’s cross looked set to pick out Steven Fletcher in the six-yard box, but Huntington touched it away from the striker and Reach could not convert the follow-up.
Preston seized the initiative with a string of chances and had a goal disallowed after an hour. Aiden McGeady’s shot was palmed away by Westwood but from the resulting corner Makienok hammered the ball home – only for the referee to blow for a foul on the keeper.
And the hosts continued to control the game, having another goal ruled out after 69 minutes when Robinson fired past Westwood but was adjudged to be offside.
Simon Grayson’s side finally got reward for their constant pressure in the 77th minute as Greg Cunningham was slipped in behind on the left edge of the area and his low cross was deflected in off the unfortunate Hutchinson.
And they came close to doubling that lead five minutes later as McGeady’s strike from 20 yards cannoned back off the post, before Tom Clarke’s close-range header was held by Westwood.
Wednesday pushed hard late on and got their reward in injury time when Reach, who was on loan at Preston last season, smashed home after a goalmouth scramble.