Rosamund Allison, 82, was found buried in debris after the storm. Doctors say she had multiple injuries and died late Thursday night.
Her death is the second in the town of Washington and the 7th in Illinois linked to the deadly storm.
A check belonging to Allison was found more than 100-miles away in suburban Hinsdale. Caroline Sutton found the check in her backyard and brought it to school.
The discovery inspired her classmates to write letters to all victims of the tornado.
Sutton and her parents delivered three vans of donated supplies along with letters from the students. They had hoped to return Allison's check and took a photo of the girl where Allison's home once stood.