United States
From Halopedia, the Halo wiki
The United States of America is a federal constitutional republic comprising over sixty districts. The country is situated almost entirely in the western hemisphere: its forty-eight contiguous states and Washington, D.C., the capital district, lie in central North America between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south; the state of Alaska is in the northwest of the continent with Canada to its east, and the state of Hawaii is in the mid-Pacific. U.S. territories, or insular areas, are scattered around the Caribbean and Pacific.
United Nations
UN
It is possible that New York City in the state of New York is the location of the supreme United Nations headquarters, commmanding the UNSC Defense Force, Colonial Administration Authority, and the Colonial Military Administration. Just like it is currently based there today.
UNSC
The UNSC probably has hundreds apon thousands of bases in the United States. Two main facilities are the ONI Chawla Base in Boston, Massachusetts. And the Tactical Autonomous Robotic Defence System Testing Facility in Chicago, Illinois.
