The Illinois Department of Healthcare and Family Services announced the incident Friday. A statement from the department says the briefcase was stolen Aug. 31 from the home of a contractor.
Confidential data in the briefcase included names, Social Security numbers, Medicaid recipient numbers and birthdates. The contractor was assessing nursing facility residents for the state.
Department representatives are visiting the nursing homes involved to meet personally with the residents affected. The department also sent them notices recommending they register for fraud alerts with consumer protection agencies.
Federal law requires agencies to notify the news media of breaches involving more than 500 people.