I am a freelance photographer, and my clients are from a dozen different states. Most of the work was actually performed in the state I live in (Tennessee), but some of it was in other states.
Example: I live in Tennessee, and did some work on location in Texas (only part of the job, since a major portion of the time is spent in Tennessee editing photos and other computer work for the client) and the client is based in Kentucky. There are half a dozen cases like this, i.e. I did a job in Alabama, but the client that paid me is in Georgia. And again, a major portion of the work was finished in Tennessee, where I live.
Do I need to file taxes in the other states, besides where I live?
I am an LLC, and file taxes as a sole proprietor.
You may need to file a tax return in the states where you worked, but it would have nothing to do with the state your client worked in. You need to visit the website of each state where you worked and see what their tax filing requirements are for a non-resident. Normally there is a minimal amount of money you can earn in a state before you have to file a tax return. If you make less than that amount, you don't need to file.