I havd been accepted to 9 schools, and I have made my choice and hit “accept”. I even applied for housing …
so my question… do I need to say “no thank you” to the others now? Or do I just ignore.
You need to decline.
Decline. If they don’t have a card to send back or an online form to fill out, email admissions and/or your admissions rep at each college. Doesn’t take long and it is the polite thing to do. As soon as possible. Good karma. 
I figured this … I just wanted to be sure. Thanks
I don’t think is common knowledge. Great advice about good karma.