I spent a few minutes going through the microfilm and have attached the three articles from the Illinois State Journal documenting the placement of all 4 of the military statues.
The first was the Infantry group, placed September 12, 1877. The Naval group was placed a day or two later. The groups are both mentioned in the same newspaper article.
The third was the Artillery group, placed April 13, 1882.
Finally, the Cavalry group was placed March 13, 1883. This newspaper article has an incorrect year, which I marked in red and included a citation for the correct year.