It marks what would have been Till's birthday.
The announcement came 71 years after the church hosted Till's open-casket funeral, a pivotal moment in civil rights history.
Today, the church is part of the Emmett Till and Mamie Till-Mobley National Monument, as well as a Chicago landmark.
The 14-year-old was falsely accused of whistling at a white woman at a grocery store in rural Mississippi.
His mother, Mamie Till-Mobley, insisted that his casket remain open so the world could see what had happened to her son.
SEE ALSO | US releases Emmett Till investigation records ahead of 70th anniversary of Chicago teen's killing
Gov. JB Pritzker said the new law will help preserve the legacy of Till and his mother.
"By signing this legislation, we ensure the lives of Emmett Till and Mamie Till-Mobley will not be forgotten. Their story will continue to be told. Their legacy will continue to challenge us to be better," Pritzker said.
Illinois Attorney General Kwame Raoul said the annual observance serves as a reminder that the work of protecting civil rights continues.
The ceremony included Rev. Wheeler Parker, Till's cousin, who was with him when he was taken in 1955.
"I wish that he was here, but he accomplished more in death than he did if he lived," Parker said. "It's mixed emotion because I think I'm pleased and happy to see the progress that has been made since, since Emmett. We've come a long way. In America, the wheels of justice grind, but they grind so slow," he said.
Organizers also noted that a rededication ceremony is scheduled for Saturday at 10 a.m. for the intersection of 71st Street and Kedzie Avenue as Mamie and Emmett Till Road.