As of May 14, 2012, the United States has a total resident population of 313,544,041, making it the third most populous country in the world. It is a very urbanized population, with 82% residing in cities and suburbs as of 2008 (the worldwide urban rate is 50.5% This leaves vast expanses of the country nearly uninhabited.^] California and Texas are the most populous states, New York City is the most populous city in the United States. The total fertility rate in the United States estimated for 2009 is 2.01 children per woman, which is below the replacement fertility rate of approximately 2.1. However, U.S. population growth is among the highest in industrialized countries since the vast majority of these have below-replacement fertility rates and the U.S. has higher levels of immigration. The United States Census Bureau shows population increase of 0.91% for the twelve-month periods ending in July 2011 Nonetheless, though high by industrialized country standards, this is below the world average annual rate of 1.092%.

There were 155.6 million females in the United States in 2009. The number of males was 151.4 million. At age 85 and older, there were more than twice as many women as men. People under 20 years of age made up over a quarter of the U.S. population (27.3%), and people age 65 and over made up one-eighth (12.8%) in 2009.^[15] The national median age was 36.8 years.^[15] Racially, the U.S. has a White American majority.

Immigrants and their u.S.-born descendants are expected to provide most of the u.S. Population gains in the decades ahead

Leading population centers
Rank	Core city	Metro area pop.	Metropolitan Statistical Area	Region[42]
1	New York City	19,015,900	New York-Northern New Jersey-Long Island, NY-NJ-PA MSA	Northeast
2	Los Angeles	12,944,801	Los Angeles-Long Beach-Santa Ana, CA MSA	West
3	Chicago	9,504,753	Chicago-Naperville-Joliet, IL-IN-WI MSA	Midwest
4	Dallas	6,526,548	Dallas-Fort Worth-Arlington, TX MSA	South
5	Houston	6,086,538	Houston–Sugar Land–Baytown, TX MSA	South
6	Philadelphia	5,992,414	Philadelphia–Camden–Wilmington, PA–NJ–DE–MD MSA	Northeast
7	Washington, D.C.	5,703,948	Washington-Arlington-Alexandria, DC-VA-MD-WV MSA	South
8	Miami	5,670,125	Miami-Fort Lauderdale-Pompano Beach, FL MSA	South
9	Atlanta	5,359,205	Atlanta-Sandy Springs-Marietta, GA MSA	South
10	Boston	4,591,112	Boston-Cambridge-Quincy, MA-NH MSA	Northeast

Marriage

In 2010, the median age for marriage for men was 27; for women, 26.

Income

In 2006, the median household income in the United States was around $46,000. Household and personal income depends on variables such as race, number of income earners, educational attainment and marital status.

Social classes in the United States lack distinct boundaries and may overlap. Even their existence (when distinguished from economic strata) is controversial. The following table provides a summary of some currently prominent academic theories on the stratification of American society:

William Thompson & Joseph Hickey, 2005
Class	Typical characteristics
Upper class (1%)	Top-level executives, celebrities, heirs; income of $500,000+ common. Ivy league education common.
Upper middle class[1] (15%)	Highly-educated (often with graduate degrees) professionals & managers with household incomes varying from the high 5-figure range to commonly above $100,000.
Lower middle class (32%)	Semi-professionals and craftsmen with some work autonomy; household incomes commonly range from $35,000 to $75,000. Typically, some college education.
Working class (32%)	Clerical, pink- and blue-collar workers with often low job security; common household incomes range from $16,000 to $30,000. High school education.
Lower class (ca. 14% - 20%)	Those who occupy poorly-paid positions or rely on government transfers. Some high school education.

total population: 78.11 years

male: 75.65 years

female: 80.69 years (2010 est.)