Commuting patterns data are tabulated from the Indiana Department of Revenue, based on the IT-40 tax returns for the year. These data provide insight into the residence and work patterns among and between counties.
Please note that the residency rules for filing the IT-40 or the forms where the state has reciprocal agreements can affect the commuting data we use from the tax forms. For example, if you were an Indiana resident at the time you enlisted in the military service, Indiana will be your home of record and you are considered to be a full-year Indiana resident for state income tax purposes during your enlistment regardless of where you are stationed. If you were stationed in another state beyond Indiana’s neighboring states, then the commuting patterns data set would show you as living in an Indiana county and commuting to work "Out of State."
Source: STATS Indiana, using Indiana Department of Revenue data