People might think there are 52 states in the Untied States because of the existence of territories such as the District of Columbia and Puerto Rico, which function similarly to states in some ways. Members of Congress have introduce bills that would admit these territories as states.
Members of Congress introduced a bill to make the District of Columbia a state in 2015, while a majority of Puerto Ricans supported statehood in a 2012 referendum. No states have been added to the United States since the additions of Alaska and Hawaii in 1959.
Puerto Rico had a population of over 3.5 million in 2014, making it more populous than 21 official U.S. states.