$200/month late fee on $1490/month commercial lease in Chicago. Is it legal?

It seems excessive, but you presumabably had an opportunity to review the terms of the lease and negociate terms before signing, so you're stuck with it now.

Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.