Reading IRS migration data: returns, people and the 20-return rule
The IRS figures count tax returns that changed county between two filing seasons. Read “returns” as households, “people” as the people listed on those returns, and remember that every county-to-county flow under 20 returns is missing from the lists.
Migration statistics usually come from surveys. The IRS files are different: they are built from the addresses on individual income tax returns. When a return filed in 2023 carries an address in a different county from the same taxpayer’s 2022 return, the IRS counts a move from the first county to the second. Nobody is asked anything, so the counts are large and precise, but they only see people who file.
Returns, people and income
Each flow comes with three numbers. The first is the number of returns, and a return is the closest thing in the data to a household: a married couple filing jointly is one return, a single filer is one return. The second is the number of people listed on those returns, the filers plus their dependents. The third is adjusted gross income, the total for all the returns in the flow, taken from the second year’s return.
Maricopa County, the home of Phoenix, shows how the pieces fit. In 2022–23, 91,952 returns arrived and 86,691 left, while 1,726,789 stayed put. The people counts run well above the return counts, because a return often lists more than one person: arriving returns in Maricopa carried 1.64 people each on average.
| Group | Returns |
|---|---|
| Returns that stayed in the county | 1,726,789 |
| Moved in from elsewhere in Arizona | 17,227 |
| Moved in from another state | 73,888 |
| Moved in from abroad or a US territory | 837 |
| All arrivals | 91,952 |
| Moved out to elsewhere in Arizona | 20,973 |
| Moved out to another state | 64,535 |
| All departures, including abroad | 86,691 |
Most of the arrivals in Maricopa came from another state: 80%, a far higher share than in Harris County, Texas (46%) or Los Angeles County, California (49%).
What the years mean
A period such as 2022–23 pairs returns filed in calendar year 2022 with returns filed in 2023. Most of those returns describe income from 2021 and 2022, and a move can have happened at any point between the two filing dates. The site uses four of these pairs, from 2019–20 to 2022–23. For the latest one the IRS adjusted how it matches returns between years, which it says brings about 5% more returns into the data, so part of any rise between 2021–22 and 2022–23 comes from the method and not from more moving.
The 20-return rule
To protect taxpayers, the IRS does not publish a county-to-county flow of fewer than 20 returns. Those small flows are pooled into catch-all lines by region, such as “other flows, different state, South”. The consequence is easy to overlook: the list of origins on a county page is never complete. A small county that sends 15 households a year to Maricopa simply does not appear on Maricopa’s list.
Across the 2,748 counties with complete totals, 8,821,132 returns moved in from somewhere else in the United States. The flows big enough to be listed account for 6,473,980 of them, or 73%. Every county profile states its own coverage; among the 285 counties with at least 40 listed origin and 40 listed destination counties it runs from 44% to 95% of arrivals.
The same rule explains why some counties have no profile at all. When one of a county’s totals falls under the threshold, the IRS withholds it, and a net figure cannot be computed. Those counties still show up as partners on the pages of the counties they trade movers with.
Who is missing
People who do not file a federal return are outside the data entirely. That leaves out many people whose income is below the filing threshold. Returns that cannot be matched between the two years are also missing, for example when a taxpayer files in one year and not the next. Children claimed as dependents move with their parents and are counted in the people column. Since the 2011–12 data, the IRS also matches a person who was listed as a dependent in the first year and files a return of their own in the second.
The address on a return is a mailing address. Most of the time it is the home, but a post office box or a preparer’s office can put a household in the wrong county.
Net figures and rates
The site’s headline number for each county is the net figure: returns in minus returns out, foreign moves included. To compare a county of 50,000 returns with one of four million, the net is divided by the number of returns filed in the county in the first year and expressed per 1,000. Maricopa’s net gain of 5,261 returns comes to 2.9 per 1,000, which places it 99th of the 285 counties with at least 40 listed origin and 40 listed destination counties.
The other measures are defined on the method page: turnover, the share of arrivals from other states, a median move distance and average incomes per return. All of them are calculated from the same IRS lines, and all of them inherit the same limits. To see the raw lists for any county, use the county tracer.
Sources
IRS Statistics of Income, SOI Tax Stats – Migration Data, county-to-county and state-to-state files, 2019–20 to 2022–23 (irs.gov). County locations: US Census Bureau, 2023 Gazetteer Files. Calculations by countymoves; definitions in How to read the data.