Legal Question in Employment Law in Illinois

"maybe". If your company has an HR department (and to be on FMLA I'll guess it does) you need to talk to them. There may be an employment policy that while you are on unpaid leave YOU are fully responsible for health care insurance premiums, or at a minimum that the employer would pay its share of the premiums but you would still be responsible for your share. Start there. If the coverage was improperly cancelled it may be capable of being reinstated, but there is no universal rule as such.