(July 2003) In June 2003, the Office of Management and Budget (OMB) released new guidelines for defining the nation’s metropolitan areas. Since the 1950s, the OMB has defined a metropolitan statistical area (MSA) as an urban core of at least 50,000 people, the county in which it is located, and adjacent counties linked by commuting patterns. Under the new definitions, the Census Bureau also identifies “micropolitan” statistical areas, consisting of urban clusters of at least 10,000 people but fewer than 50,000 people.

By applying these 2003 definitions to county-level population data for 1950 and 2000, we can track long-term changes in the population living in metro, micro, and nonmetro counties.

What these data show is a major shift in the age composition of the population living outside of metropolitan areas. The number of children living “outside core-based statistical areas” dropped from nearly 7 million in 1950 to 5 million in 2000, a 37 percent decrease. In the United States, as a whole, the number of children increased by 34 percent — with almost all of gains occurring in metropolitan counties. In 1950, about 71 percent of the population under age 18 lived in metropolitan areas; that percentage increased to 83 percent in 2000. The share of children living outside core-based statistical areas was cut in half — from 14 percent in 1950 to only 7 percent in 2000.

Most of the population growth in metropolitan areas has occurred in the suburbs. Over the past 50 years, many people have moved from rural areas (and cities) to suburban communities in order to find work and start families. Although the population in many rural communities has rebounded in recent years,1 the population has grown the fastest in suburban areas and “exurban” communities located at the fringes of metropolitan areas.2 Families are attracted to the suburbs because of the good schools, stable communities, economic opportunities, and other urban amenities that often characterize these areas.

Kelvin M. Pollard is a research demographer and Mark Mather is a policy analyst at the Population Reference Bureau.


  1. Kenneth M. Johnson, The Rural Rebound, PRB Reports on America 1, no. 3 (1999).
  2. Mary M. Kent et al., “First Glimpses From the 2000 Census,” Population Bulletin 56, no. 2 (2001): 19-25.