The United States is a traditional government established on Old Earth. In the time of the Universal Year, however, the United States has re-established itself as a permanent galactic super power after a cycle of downturns and upturns as a "super power" in Old Earth's heyday.
The United States saw the relocation as a reset on power within the human collective and took full advantage of that. The United States has begun claiming whole systems as part of the "new" United States -- because of this, some call it the United Systems. The customary "of America" was dropped once the government moved off Old Earth.
Currently, the home base of the United States is the Washington System. Each progressive system taken under "control" of the United States follows closely the naming pattern of the original States annexation into the original United States, as well as many territories it held. The "North," "South," "East," and "West," of any states are cut out since those directions are not commonly used in space. The current list is as follows:
America, Columbia, Delaware, Pennsylvania, New Jersey, Georgia, Connecticut, Massachusetts, Maryland, Carolina, New Hampshire, Virginia, New York, Rhode, Vermont, Kentucky, Tennessee, Ohio, Louisiana, Indiana, Mississippi, Illinois, Alabama, Maine, Missouri, Arkansas, Michigan, Florida, Texas, Iowa, Wisconsin, California, Minnesota, Oregon, Kansas, Nevada, Nebraska, Colorado, Dakota, Montana, Idaho, Wyoming, Utah, Oklahoma, New Mexico, Arizona, Alaska, Hawaii, Puerto Rico, Guam, Mariana, Samoa, Wake, Midway, Baker, Howland, and Jarvis.
The United States would be sure to be able to pull more names out from its history if needed. President's last names would be anticipated to be next on the list.