The Chicago Transit Authority operates its services on a varied schedule depending on the mode of transportation. For the 'L' trains, they generally run from approximately four in the morning until about one in the morning the following day. Specific hours can vary by line and day of the week, so it is wise to check the schedule for the line you plan to use.
As for the bus services, most routes typically operate from early morning around five or six until late at night, and some routes are available 24 hours a day.
To ensure the most accurate and up-to-date information regarding the hours of operation for specific routes and services, it is advisable to check the current web page on the official Chicago Transit Authority website. This will provide you with detailed schedules and any potential changes that may occur.