McCormack played an integral part in Leeds' equaliser, as Luke Varney crashed home to level David McGoldrick's 11th-minute opener, before the striker celebrated his recall to the Scotland squad with a winner three minutes after the restart.
McCormack has been the subject of a reported three bids from Middlesbrough but McDermott is unwilling to sell given his importance to the side.
The manager explained: "Ross is a quality player who scored a quality goal.
"I don't know how many bids we have had - I leave that to the owners and the player's agent. But I want him to stay and Ross wants to stay.
"I think selling him to another Championship club sends out the wrong message."
Aside from praising his striker, whose talks over a new deal at Leeds to warn off potential suitors continues, McDermott was equally delighted with his side's gutsy performance.
Ipswich dominated the first 25 minutes, scoring with a lethal 20-yard finish from McGoldrick and then seeing a lovely curling effort from left-back Aaron Cresswell cannon off the crossbar.
But after Varney equalised and McCormack grabbed a winner that Leeds overall deserved, McDermott said: "They were on top for the first 25 minutes and we had to change our shape in the second half.
"We have been 1-0 down (in three league games) this season, but that happens in football. There is good resilience and desire in the dressing room I thought we were good value for the result."
Town boss Mick McCarthy was disappointed his side didn't capitalise further during the dominant opening throes of the match - and also admitted his keeper Scott Loach came in and apologised to the dressing room after reacting slowly to McCormack's skidding winner.
McCarthy said: "We should have put them to the sword when we were on top in the first half.
"But then they got a fortuitous equaliser which changed the course of the game.
"The second goal was a real poor one to concede, from the moment we gave the ball away to the shot.
"He (Loach) came in and apologised - he should have saved it and he knows that. There is no point dancing around the issue."
As his own side reflect on a tough Championship start that has seen them accrue just three points from a possible 12, McCarthy paid tribute to their opponents.
He added: "Leeds have got some good experienced players and the front three (Varney, McCormack and Noel Hunt) are a real handful.
"They defended doggedly in the second half but we should have made them pay in the first half.
"If it had ended up 1-1, we would have taken that."