40 ILCS 5/15-127
"Surviving spouse": (a) The surviving wife or husband of a participant, but only if she or he (1) is the mother or father of the participant's son or daughter, (2) legally adopted the son or daughter while married to the participant and while the son or daughter was under age 18, (3) was married to the participant at the time both of them legally adopted a child under age 18, or (4) was married to the participant for not less than one year immediately prior to the day the participant died; and (b) The surviving wife or husband of an annuitant, if their marriage occurred at least one year prior to the date the annuitant died. The change in this Section made by Public Act 82-478 shall be applicable to annuitants whose employment status terminated before September 15, 1981 as well as those who terminate employment after that date but not to annuitants who pass away before that date.
40 ILCS 5/15-127