Born inside the United States
Birth certificates are maintained by each state for the people who are born in that state. Contact the county or state vital records in the state where you were born to get a copy of your birth certificate. There is a website that can help you find out where you should write for vital records across the United States.
Born outside the United States
If you were born outside the United States and your parents were United States citizens at the time of your birth, you can write to:
U.S. Department of State
Washington Passport Agency
1111 19th Street NW
Suite 300
Washington, DC 20522-1705