I'm not sure if you need/want to state that you are a US citizen on your resume.
However, it will very important to HR if you are or aren't a US citizen. Many companies will only hire US citizens or individuals who are authorized to work in the US. I don't think they just want to deal with having to get authorization for a potential employee.
You should do some research on the company you're interested in and see if they have any sort of policy on citizenship.