The U.S. attorney's office said Crundwell will change her plea to guilty Wednesday, WHBF-TV, Rockford, reported.
"Knowing the facts, I don't know how she could ever be found innocent," Dixon Mayor Jim Burke told the TV station.
Authorities allege Crundwell stole the millions of dollars over two decades and spent it on luxuries. After she was arrested in April, however, she asked for a public defender, saying she was too broke to hire one.
"The whole thing is a pity. It's a tragedy of major proportions for her and the community," Burke said. "No matter what happens here her life is pretty much ruined. You can never say never, but she's got an awful bleak future staring her in the face."
Federal authorities will eventually sell off Crundwell's assets but the mayor said the city will never see the full $53 million.
"When this is all over the city is going to be in good financial shape and we will move on, put this behind us and get back to focusing on the great positive characteristics we have in this community," he said.