The Bureau of the Census defines a place as a concentration of population; a place may or may not have legally prescribed limits, powers, or functions. This concentration of population must have a name, be locally recognized, and not be part of any other place. A place either is legally incorporated under the laws of its respective State, or a statistical equivalent that the Census Bureau treats as a census designated place (CDP). Each State enacts laws and regulations for establishing incorporated places. The Census Bureau designates criteria of total population size, population density, and geographic configuration for delineating CDPs. Not everyone resides in a place; in 1990, approximately 66 million people (26 percent) in the United States lived outside of any place, either in small settlements, in the open countryside, or in the densely settled fringe of large cities in areas that were built-up, but not identifiable as places.
A "town" is a human settlement or urban area that has a name, defined boundaries and a local government. Towns are generally larger than villages and smaller than cities. A "small town" is a place whose population is in three digits. A "medium" town has a population between 1,000 and 10,000. A "large" town has a population between 10,000 and 100,000. Common population definitions for an urban area (city or town) range between 1,500 and 50,000 people, but some states follow different guidelines. A "metropolis" is the capital or chief city of a country or region, or: a very large and densely populated industrial and commercial city. A county is an administrative or political subdivision of a state that consists of a geographic region with specific boundaries and usually some level of governmental authority.
Of the nation's 328.2 million people, an estimated 206.9 million (about 63%) lived in an incorporated place as of July 1, 2019. About 76% of the approximately 19,500 incorporated places had fewer than 5,000 people. Of those, almost 42% had fewer than 500 people. On the other hand, only 4.0% (780) of all cities had a population of 50,000 or more in 2019, yet nearly 39% of the U.S. population (127.8 million) live in those cities. 48 out of the 50 states use counties. Louisiana calls its counties parishes while Alaska got rid of counties and only uses boroughs.