Chicago-native Jeremy Roscoe, a 6-foot-3 guard, signed his letter of intent to SIU late Wednesday night.
Roscoe said his relationship with graduate assistant coach John Clancy helped guide him to SIU.
"I used to work out with him every Saturday when I was in high school," Roscoe said. "So when he got the job, he made me pay attention to the program, and I fell in love when they started having a great start."
SIU is coming off a 22-10 season, its best since the 2006-07 Sweet 16 season.
Roscoe won the 2015 IHSA Class 2A state championship at Uplift Community High School, averaging 14.