The headquarters of the National Aeronautics and Space Administration (NASA) is in Washington DC, but its primary launch sites are at the Cape Canaveral Air Force Station in Florida and the Vandenberg Air Force Base in California. NASA has research centers, laboratories, space centers and flight centers in California, New Mexico, Texas, Mississippi, Alabama, Florida, Virginia, West Virginia, Ohio and New York.
NASA headquarters is located in Washington DC. However, there are several facilities throughout the US. Eleven stations and research facilities are located in different areas and many of them may be open for tours and visits.
NASA is located in a number of cities across the United States. Its most famous location is the Johnson Space Center 1601 NASA Parkway, which was formerly NASA Rd 1, Houston, Texas 77058. Houston is home of the Mission Control Center which monitors all humans in space for the United States from lift off til landing. You can see more of the locations of NASA here: http://www.nasa.gov/about/sites/index.html