Geographical Mobility/Migration

The American Community Survey (ACS) and the Puerto Rico Community Survey (PRCS) ask respondents age 1 year and over whether they lived in the same residence 1 year ago. For people who lived in a different residence, the location of their previous residence is collected.

ACS uses a series of monthly samples to produce estimates. Estimates for geographies of population 65,000 or greater are published annually using these monthly samples. Three years of monthly samples are needed to publish estimates for geographies of 20,000 or greater and five years for smaller geographies. The 5-year dataset is used for the county-to-county migration flows since many counties have a population less than 20,000. The first 5-year ACS dataset covers the years 2005 through 2009.

In addition to the county-to-county flow files, there are similar files that substitute minor civil divisions (mcd), in place of counties, for states where they serve as general-purpose local governments. These states are Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin.

• Documentation and Analysis 
  • 2012-13. How do the ACS five-year migration data compare to the 2000 Census migration data? [PDF - 1.7M] , by Megan Benetsky, William Koerber. Issued 05/2012.
  • 2012-06. 2005-2009 American Community Survey County-to-County Migration Files [DOC - 4.0K] [PDF - 4.0K] Issued 03/2012.
  • Expanded Tables [XLS - 4.0K]
• County-to-County Migration Flows 
  • Inflow [XLS - 4.0K]
  • Outflow [XLS - 4.0K]
  • All flows [TXT - 4.0K]
• County/MCD-to-County/MCD Migration Flows  
  • Inflow [XLS - 4.0K]
  • Outflow [XLS - 4.0K]
  • All flows [TXT - 4.0K]
  • ACS Migration Flow User Note: Omission of MCD flows within same county [PDF - 4.0K]

Table Notes:
Sample size and data quality measures (including coverage rates, allocation rates, and response rates) can be found on the American Community Survey website in the Methodology section.

Data are based on a sample and are subject to sampling variability. The degree of uncertainty for an estimate arising from sampling variability is represented through the use of a margin of error. The value shown here is the 90 percent margin of error. The margin of error can be interpreted roughly as providing a 90 percent probability that the interval defined by the estimate minus the margin of error and the estimate plus the margin of error (the lower and upper confidence bounds) contains the true value. In addition to sampling variability, the ACS estimates are subject to nonsampling error (for a discussion of nonsampling variability, see Accuracy of the Data). The effect of nonsampling error is not represented in these tables.

Other Sources

Inmigration and outmigration data are available for published geographies in American FactFinder. Detailed tables B07001 through B07013 contain geographical mobility in the past year for current residence by selected characteristics for all summary levels. The data are separated into five geographical mobility categories: Nonmovers, movers within the same county, movers from a different county within the same state, movers from a different state, and movers from abroad. Detailed tables B07401 through B07413 contain geographical mobility in the past year for residence 1 year ago by selected categories for some summary levels. The data are separated into four categories: Nonmovers, movers within the same county, movers to a different county within the same state, and movers to a different state. Tables dealing specifically for Puerto Rico have a -PR suffix and slightly different geographical mobility categories

The Population Estimates Program publishes intercensal population estimates using various administrative and survey data. They produce population, population change, and estimated components of change files for the nation, states, counties, metropolitan and micropolitan areas, and combined statistical areas as part of the whole data set they provide to download for analysis. The files contain estimates for net internal and net international migration.

Contact Information

For more information or comments about current or future ACS county-to-county products, contact Alison Fields, Chief, Journey-to-Work and Migration Statistics Branch at alison.k.fields@census.gov or 301.763.2454

• ACS Background Information
• ACS Public Use Microdata Sample (PUMS) Files Information
• State-to-State Migration Flows
• Population Estimates Program