I will be traveling to thailand in about a month and was wondering if I needed to apply for a tourist visa in my hometown of Chicago. I have heard that US citizens can apply for a 30 day visa for free after landing in Suvarnabhumi...

As a US citizen you do not need any visa at all to travel to Thailand for 30 days or less.

When you arrive in Bangkok you will get what a 30 day stamp which tells you the exact date you must leave Thailand. It will be 30 days after you arrive. There is no need to apply for or buy any visa if you keep it 30 days or less.

Thank you!

Keep in mind that the 30 days includes the day you arrive and get stamped. It is important to check the date on the stamp before walking away from Immigration. They CAN make the occaisonal mistake.

Also consider if you arriving late at night and the international date line. If you are cutting it real close you want to know the date they will see you as arriving, it won't be the same day as when you leave Chitown.