(November 2011) Exactly 50 years ago, geographer Jean Gottmann coined the term "megalopolis" to describe the sprawling regional mega-city taking shape between Boston and Washington, D.C., gobbling up rural areas in its wake.1

"BosWash" is the nickname futurist Herman Kahn gave this potentially 400-mile urban area in the late 1960s. He called the urbanizing swath from Chicago to Pittsburgh along the Great Lakes and Ohio River "ChiPitts," and the California coastal development stretching from San Francisco to San Diego "SanSan."2

In a 1967 book, he predicted that by 2000 one-half of the U.S. population would live in those three megalopolises and that any examination of U.S. population trends in the 21st century "would largely be a study of BosWash, ChiPitts, and SanSan."3

But a somewhat different story has unfolded over the past 50 years, says Mark Mather, co-author of PRB's Reports on America: First Results From the 2010 Census. "The three megalopolises' share of U.S. population actually declined somewhat between 1960 and 2010," says Mather. "Rather than growing to encompass one-half of the U.S. population, the three areas are only home to about one-third of all U.S. residents."

Three Megalopolises, Population 1960 and 2010, and Percentage of U.S. Total Population

  1960 Population % of U.S. Total 2010 Population % of U.S. Total
Total U.S. Population 179,323,175 100 308,745,538 100
  BosWash 37,152,310 21 51,770,596 17
  ChiPitts 13,537,469 8 17,719,657 6
  SanSan 12,180,125 7 26,745,198 9
Total Share   36   31

Note: See References below for definitions of the megalopolises.
Sources: U.S. Census Bureau, 1960 Census of the Population, Vol. A, Part 1 (Washington, DC: Government Printing Office, 1961) and for 2010 Census data, PRB's DataFinder, accessed at www.prb.org/DataFinder.aspx, on Oct. 24, 2011. 

Mather and his co-authors highlighted several key population trends that observers in the 1960s had not fully anticipated:

The U.S. population has shifted to the South and West since the 1950s. Today the South is the most populous region, followed by the West, Midwest, and Northeast. In 2010, the West overtook the Midwest as the second most-populous census region—just as it overtook the Northeast in 1990.

Old industrial cities in the Northeast and Midwest–often called the Rust Belt—lost population, as manufacturing declined and people left in search of better jobs. Many metro areas in ChiPitts–such as Detroit, Buffalo, Cleveland, and Pittsburgh—have been plagued by high rates of out-migration since the 1970s.

The fastest growing areas have been mainly outside the three megalopolises. These fast-growing areas included suburbs of metropolitan areas in the South and West, such as the region around Orlando, Fla.; the "Research Triangle" area of North Carolina; and the areas surrounding such cities as Las Vegas, Atlanta, and several cities in Texas (Houston, Dallas-Fort Worth, San Antonio, and Austin). The northern Virginia exurbs of Washington, D.C. —at the southern end of BosWash—are an exception.

Population aging has fueled growth in retirement destinations, which tend to be outside the three metropolises. During the 2000s, retirement-destination counties—ones that are attractive to people age 60 and older—were among the big demographic "winners." One-third of the 440 retirement counties grew at least twice the national average between 2000 and 2010. Two of the large, fast-growing retirement destinations are Maricopa County, Arizona, and Clark County, Nevada. 

But Gottmann's main message—sprawling urban growth– reflects population dynamics still at play today, Mather noted:

  • The U.S. population shifted from rural areas to urban and suburban communities, a trend begun in the 1930s. Today more than 80 percent of U.S. residents live in metropolitan areas. The U.S. metropolitan population grew 11 percent during the 2000s, more than double the rate for areas outside metros. Metros in the South and West grew fastest, while the metro population in the Northeast and Midwest increased at less than half the national rate.
  • Within metropolitan areas, most U.S. population growth during the past century has taken place in suburban areas, rather than central cities. By 2010, 51 percent of the population lived in suburbs, compared to 31 percent in 1960. The share of the population living in central cities has remained fairly constant; it was 32 percent in 1960 and is 33 percent today.
  • The rural population has shrunk dramatically, as rural areas have lost population or have been swallowed up in sprawling nearby metropolitan areas. The rural areas that have seen significant population losses in recent decades include much of the Great Plains and northern and central Appalachia. In fact, nearly half of the 1,104 counties that lost people during the 2000s were counties that were isolated from metropolitan areas and had small or nonexistent urban populations.

Paola Scommegna is senior writer/editor at the Population Reference Bureau.


  1. Jean Gottmann, Megalopolis: The Urbanized Northeastern Seaboard of the United States (New York: The Twentieth Century Fund, 1961)
  2. Herman Khan and Anthony J. Wiener, The Year 2000: A Framework for Speculation on the Next Thirty-Three Years (New York: Macmillan, 1967): 61.
  3. Kahn and Wiener, The Year 2000. 
  4. The megalopolises grew during the 50-year period to encompass previously rural adjacent counties: BosWash includes metro Boston, New York, Philadelphia, Baltimore, and Washington, D.C., plus many adjacent counties identified in Gottmann's original analysis; ChiPitts includes metro Chicago, Pittsburgh, Cleveland, Buffalo, Akron, Toledo, and Detroit; and SanSan includes metro San Francisco, Santa Barbara, and San Diego.