Claim: Massachusetts is one of 4 US commonwealths.

A U.S. state is a constituent political entity of the United States of America . There are 50 states , which are bound together in a union with each other . Each state holds governmental jurisdiction over a defined geographic territory , and 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 -LRB- e.g. , paroled convicts and children of divorced spouses who are sharing custody -RRB- .   States range in population from just under 600,000 -LRB- Wyoming -RRB- to over 39 million -LRB- California -RRB- , and in area from 1214 sqmi -LRB- Rhode Island -RRB- to 663268 sqmi -LRB- Alaska -RRB- . Four states use the term commonwealth rather than state in their full official names .   States are divided into counties or county-equivalents , which may be assigned some local governmental authority but are not sovereign . County or county-equivalent structure varies widely by state . State governments are allocated power by the people -LRB- of each respective state -RRB- through their individual constitutions . All are grounded in republican principles , and each provides for a government , consisting of three branches : executive , legislative , and judicial .   States possess a number of powers and rights under the United States Constitution ; among them ratifying constitutional amendments . Historically , the tasks of local law enforcement , public education , public health , regulating intrastate commerce , and local transportation and infrastructure have generally been considered primarily state responsibilities , although all of these now have significant federal funding and regulation as well . Over time , the U.S. Constitution has been amended , and the interpretation and application of its provisions have changed . The general tendency has been toward centralization and incorporation , with the federal government playing a much larger role than it once did . There is a continuing debate over states ' rights , which concerns the extent and nature of the states ' powers and sovereignty in relation to the federal government and the rights of individuals .   States and their residents are represented in the federal Congress , a bicameral legislature consisting of the Senate and the House of Representatives . Each state is represented in the Senate by two senators , and is guaranteed at least one Representative in the House . Representatives are elected from single-member districts ; seats in the House are distributed among the states in proportion to the most recent constitutionally mandated decennial census . Each state is also entitled to select a number of electors to vote in the Electoral College , the body that elects the President of the United States , equal to the total of representatives and senators from that state .   The Constitution grants to Congress the authority to admit new states into the Union . Since the establishment of the United States in 1776 , the number of states has expanded from the original 13 to 50 . Alaska and Hawaii are the most recent states admitted , both in 1959 .   The Constitution is silent on the question of whether states have the power to secede -LRB- withdraw -RRB- from the Union . Shortly after the Civil War , the U.S. Supreme Court , in Texas v. White , held that a state can not unilaterally do so .