The hosts, who sacked manager Brian McDermott yesterday, made a good start with McCormack at the centre of their first promising attack, which ended with Cameron Stewart going close to opening the scoring.
However, the Terriers began to find their own feet with their strike partnership of Nahki Wells and Danny Ward both going close with efforts at goal.
Mark Robins's side started to impose themselves on the game with Oliver Norwood seeing his shot come back off the post, while Leeds struggling to repel the waves of attack.
Huddersfield then took a deserved lead midway through the first half when Calum Woods found Ward, and his left-footed shot found the bottom corner of Paddy Kenny's net.
As the half drew to a close, United looked for a response and began to test the Terriers defence with McCormack and Rodolph Austin both going close from the hosts.
The visitors kept pushing forward, though, and Norwood almost doubled their lead when his effort forced a save out of Kenny.
However, it was Leeds who found an equaliser in first-half stoppage time when Sam Byram's cross reached McCormack, who tucked the ball past Alex Smithies to the relief of the Elland Road faithful.