United States

The United States of America was a federal constitutional republic comprising over sixty different districts. The country was situated almost entirely in the western hemisphere: its fifty contiguous states (four of which being technically commonwealths), and Washington, D.C., the capital district, lay 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 north-west 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. As of the present, it has the third largest population on Earth, and the largest economy on Earth. As of 2525, the United States has formed a loose association with Mexico and Canada to form the United Republic of North America.

United Nations
It is supposed that New York City in the state of New York is the location of the United Nations supreme headquarters, commanding the UNSC Defense Force, Colonial Administration Authority, and the Colonial Military Administration as it was currently based there in the 21st century. However HIGHCOM, the High Command of the UNSC is based in Sydney, Australia. It may have been reorganized upon the formation of the United Earth Government into the United Republic of North America. United Nations Space Command Supreme Headquarters is known to be situated somewhere in the United Republic of North America.

United Nations Space Command
The UNSC probably has hundreds of bases in the United States. One such facility is the ONI Chawla Base in Boston, Massachusetts. Although, many more have been mentioned.

United Republic of North America
The United States, along with Canada and Mexico, have formed the United Republic of North America. However, the time of the formation is currently unknown.

Locations Of Note

 * Chawla Base in Boston was an ONI-controlled and directed UNSC base that held the Deep-Space Artifact the Covenant were after.
 * Cleveland was one of the locations attacked by the Covenant during the Battle of Earth.
 * Tactical Autonomous Robotic Defense System Testing Facility in Chicago, Illinois, which forms the Multiplayer level Foundation of Halo 2
 * New York is an important location on one of the ILB stories and it's also home to some of the main characters.
 * Sergeant Avery Johnson grew up in the Greater Chicago Industrial Zone (formerly Chicago, Illinois).

Possible Dissolution
Evidence suggests that by the 26th century, the United States no longer existed as a political entity. This is supported by the Halo Encyclopedia, which describes the United Republic of North America as being composed of Canada, Mexico, and "the political remnants of the United States," suggesting a dissolution of the Union.

Additionally, in his report on Admiral Preston Cole, Codename: SURGEON makes reference to the Battle of Gettysburg, which he describes as taking place during "the first American Civil War." This wording strongly suggests that there was in fact at least one more civil conflict, which may or may not have resulted in the dissolution of the Union. It is important to note that the word "first" is not capitalized, indicating that that is not the formal name of the war (unlike, for example the First World War). Therefore if a second civil conflict did take place, it would almost certainly go by a name other than the "Second American Civil War."

Trivia

 * Although many other countries in the Halo universe have undergone radical change both politically and territorially, the United States would appear to have maintained some element of its sovereignty following the rise of the United Earth Government. Though this is not explicitly stated in Halo canon, in I Love Bees Rani Sobeck makes direct reference to the Fifth Amendment, implying that the Constitution is still the foundation for law in 26th-century America. This is further supported by the continued existence of the IRS, and several characters in Halo canon being described as Americans.