I found a good link which lists how to go about filing for a DBA in each state. Several have links listed to go directly to state websites. I was able to do it completely online.
I wish I could have done mine entirely online! I had to go down to the courthouse to register mine with the clerk, and with all the increased security, that's always a pain!
Thanks for the link, I am in Illinois and although i have my business license, I should have gotten an assumed name first. I think I'm working backwards.