Mayor Daley appointed a new inspector general to replace David Hoffman, who resigned to pursue a Senate run.
Ferguson has a measure of Illinois clout already. He prosecuted the husband of Democratic Rep. Jan Schakowsky on bank fraud and federal tax violations.
Hoffman, who had a reputation for being an aggressive investigator into waste and corruption at City Hall, praised Ferguson's selection Friday. He said Ferguson has an excellent reputation in the U.S. attorney's office.