Defender O’Connell’s new contact - until 2023 - comes after new deals to secure the futures of top scorers Billy Sharp and David McGoldrick, plus wing-back Enda Stevens.
And for manager Wilder, the new deals are evidence of the value of the squad - and to fend off interest from rival clubs - he has built since returning to the Blades in 2016.
“To have Jack sign an extension to his contract is great news, it’s reward for Jack in terms of his performances since he came to the football club,” said Wilder.
“He plays like a leader, he plays like a warrior, that will to win.
“It’s been a really good fit. I am delighted that Jack, alongside, Billy, Enda and David McGoldrick have recently re-signed and part of this club going forward.
“These players are under contract and we have got assets at this football club now.
“This is what we talked about when I came in, I didn’t see there were many assets when I walked through the door.
“Now you look through the group - not that I want a fire sale - but you have assets right the way through.”
O’Connell, 24, is available for selection for Monday’s Steel City derby after being sidelined with a hamstring injury.
With fellow defenders John Egan and George Baldock also fit, Wilder has some tricky selection issues ahead of the trip to Hillsborough.
“There’s some real tough decisions to be made,” he said.
“Not just picking the XI, but picking the substitutes and leaving some good players out of the 18.”