Generally, you must file your Small Claims action in the county where
1) the defendant resides, or
2) where the events happened which you believe give you the right to sue, e.g., where the accident occurred, contract was signed or leased premises located.
A corporation is considered to reside in any county where it does business or has an office. (735 ILCS 5/2-102). Filing the claim in the wrong county may result in the case being dismissed. If you are not sure which county could be the correct location for your Small Claims action, consider talking to a lawyer.