Can Chicago make me pay $100 for a red violation that happened 5 months ago?

of course it is legal if you were ticketed. Shouldn't have run the red light. Statutes run for some time. If it had bee 3 or more years and not charged then probably not legal. Once charged they go forward but justice is slow. If had big suit could be years before settled.

You had an option to pay your fine in the mail. You had an option to go to court to plead guilty or not guilty. You didn't show up. No show means guilty, you lose. They could have issued a warrant and taken you to jail. Instead they are giving you 21 more days to pay up. If you don't you will have a warrant for your arrest and go to jail I would expect.

If you did not receive a ticket, is a camera citation, then you are going to have to pay if you got the ticket and had option of going to court and did

Not. In some cases camera citations by cities have had problems as the state may claim only they control traffic, ESP. on state hwys.

For $100 you can't afford to fight it as attorney will cost you more than that for an hour let alone the several or more hours. If what you received allows you to plead and you didn't miss a court date, plead no contest rather than guilty. There is a bit of difference. If you really want legal advice you see an attorney in your own state who is only ones who can give you legal advice. You won't get it here as there are too many missing details for even an attorney to advise you and they get their fee. If you have an appeal process on your document (only if you didn't have opportunity earlier then you can do that but may incur more court costs.

Actually $100 for running a red light is small potatoes. If this is all a surprise, go pay in person. I am assuming it isn't a scam and wanting you to mail money to a PO box. But having 21 days is not usual scam language. Scans give you a day or two and threaten arrest and you never rsn a red light. I think you did or you would have said so. I tried to address all situations I could think of since you didn't state all the facts.

DUH.

Read the ticket. You had a certain amount of time to respond to the charge. You could have plead guilty and sent in the money. You could have showed up at court and plead not guilty. Seems to me you did neither. So after a certain amount of time of not hearing from you either way, they automatically found you guilty and sent you the fine. If you do not pay it, they will issue a bench warrant. Nothing will happen until you get caught again doing something. The cops will run your drivers license number, the bench warrant will come up and they will arrest you. Then you will have to post several hundreds of dollars in bail and will have to show up in court to resolve the whole issue. By the time it is over, you will be out about $500.

Pay the money and stop running red lights.