The Illinois Federation of Teachers represents more than 100,000 members.
About one-third of its members are also members of the Chicago Teachers Union.
"I'm very proud of this, this helps my campaign a lot," Dillard said. "Our Dillard campaign is on a great trail of momentum. And things are going very, very well."
This is only the second time in the IFT's history that it is endorsing a Republican candidate for governor.
Dillard has said education will be a top priority for his administration.