A state of the United States of America is one of the 50 constituent political entities that shares its sovereignty with the United States federal government. Due to the shared sovereignty between each state and the federal government, Americans are citizens of both the federal republic and of the state in which they reside. State citizenship and residency are flexible and no government approval is required to move between states, except for persons covered by certain types of court orders (e.g., paroled convicts and children of divorced spouses who are sharing custody). States range in population from just under 600,000 (Wyoming) to over 38 million (California). Four—Kentucky, Massachusetts, Pennsylvania, and Virginia—use the term commonwealth rather than state in their full official names.