The $275 million project is funded by the Rebuild Illinois Capital Program.
That route was discontinued in 1981.
Governor J.B. Pritzker discussed the impact the project will have on Illinois at a news conference Thursday.
"The new Rockford intercity passenger rail service will have a positive economic impact that will strengthen Northern Illinois for years to come. From the hundreds of construction and engineering jobs created by our planned rail improvements, to the increased economic growth that comes with heightened connectivity, all the way to the long-lasting reduction in pollution and traffic congestion that will stem from more efficient rail service to driving," Pritzker said.
The first trains on that route are expected to start running in late 2027 with several stops between the two cities also scheduled.