Mulligan was living in a retirement home in Des Plaines and had been declining healthwise, but Cosgrove did not know the immediate cause of Mulligan's death.
Governor-Elect Bruce Rauner expressed sadness upon hearing the news. “Diana and I offer our heartfelt condolences on the passing of former State Representative Rosemary Mulligan. Rosemary was a tireless advocate for her district, a defender of the taxpayer and a champion for Illinois women. She was a true public servant whose legacy will continue to guide us for years to come.”
Mulligan was a leading abortion advocate all the twenty years she was in the Illinois legislature. When she was elected to the Illinois House in 1993, when she beat by six votes the incumbent outspoken pro-life lawmaker Penny Pullen in a Republican primary challenge.
Their 1992 election court challenge established familiarity with "hanging chads" and voting abnormalities that were to be referred to in the Bush vs. Gore 2000 challenge in Florida.