There are many explanations for why some people erroneously believe that there are 52 states in the United States. The most likely explanation is that some people simply confuse some United States territories and districts as states.
Washington D.C., the capital city of the United States, is commonly misidentified as a state, and it is typically included in lists of U.S. states even though it is not. Instead, its status is that of a federal district, and it also does not have voting representation in congress. The founders of the United States believed that the capital city should be set apart from all the states and governed by congress. Although there have been movements in recent years to push for statehood, Washington D.C. remains a federal district as of 2015.
Confusion also surrounds the status of Puerto Rico, a commonwealth that the United States has controlled since the early 20th century. The confusion grew even more during the early 2000s, when a significant push for the pursuit of statehood emerged. As of late 2014, more than half of Puerto Rico's residents supported statehood. Other territories that some people erroneously refer to as U.S. states include Guam, American Samoa and the U.S. Virgin Islands.