Geographical mobility examined: Fairfax county, VA

Living in Fairfax county VA, I meet with a lot of people who have moved here from someplace else in the recent past – some from other parts of the US and quite a few from other parts of the world. People are moving out as well – anecdotally, mostly to neighboring Loudoun county VA, in search of more affordable housing options.

I thought it would be interesting to look at these movements using data published by the American Community Survey (ACS), specifically the 2010-2014 ACS county to county migration flows. This was the most recent 5 year data set by ACS available on the Census website and was hence the one used for this analysis. (Note that 2011-2015 ACS data is scheduled to be made available December 8th, 2016)

How does the ACS get these migration flow numbers?

(courtesy the Census website)

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.

Starting with the 2009-2013 5-year products, additional metropolitan statistical area-to-metropolitan statistical area tables are included.

The Analysis I: Where are people coming from?

The immigration rate for Fairfax city came out to be 7.65%. And where are people coming from? It turns out, just about everywhere! That’s right, we had people come in from each of the 49 other states, the District of Columbia and Puerto Rico; we’ve had people from Asia, Europe, Africa, South and Central America, other parts of North America, U.S. Island areas and Oceania!

The chart below shows what the distribution looks like – the percentages refer to what part of the total immigrants come from each region. The grouping is a bit “non-standard” in that for within the U.S, states are grouped together; and for outside the U.S, continents are grouped together. Additionally, the U.S. Island areas, Puerto Rico, D.C, Caribbean Islands and Central America are each a separate category. This is the way place of origin is called out in the ACS data, so that’s what we will show as well.

Not surprisingly, the largest of these groups (34%) is from within Virginia, from counties other than Fairfax county. The next largest group is people from the continent of Asia (11%), followed by Maryland (7%) , Europe and California.

Within Virginia, our neighboring areas – Arlington county, Alexandria city, Loudoun county, Prince William county and Fairfax city are where people are mostly moving in from; though there is movement from another 80 counties/cities within the state.

The Analysis II: Where are residents going to?

People are moving out as well – The out migration rate at 7.06% is just a little less of the immigration rate. And their next state of residence? For 54% it is still Virginia, followed by Maryland and then California, Texas, Florida and North Carolina. But it does not stop there – the remaining 25% move to one of the other 46 States or D.C or Puerto Rico. As with the immigration, there is someone going to each one of these states.

 Of those who move to other counties within Virginia, it seems that Prince William county, Loudoun county, Arlington county and Alexandria city are the preferred destinations.

So there you have it, that’s what mobility data for Fairfax county looks like.

Note: This ACS data set comes with margin of errors at 90% confidence levels; these were not used for the purposes of this analysis

This post has been cross posted on


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