Is this a short form citation? If not (which is my assumption), use a comma rather than "at" between the first page and the pincite. "144 Ill. 2d 339, ___ (1991)."
Correct. And if it is, then you use the at but omit the starting page and year:
"144 Ill. 2d at ___."
Also, don't cite to Ill. 2d. Cite to N.E. or N.E.2d, if therein.
The correct long cite is:
579 N.E.2d 873, ___ (Ill, 1991). (ETA: This is wrong, see below)
The correct short cite is:
579 N.E.2d at ___.