If my state in Box15 is "Guam," but I'm active duty military, what do I put as my Employer's State ID Number?

If Guam is listed on your military Leave and Earnings Statement, that indicates your Home of Record and/or State of Legal Residence (SLR) is Guam.    If so, your income tax filing is a little different.   If you are active duty military, you file state taxes in your SLR.

If you use TT to prepare (but not file) your Guam tax return, choose "Foreign or US possession" as your state of residence.  It is at the bottom of the state of residence drop-down list in the My Info section.   Please see this community discussion for information on filing a Guam return.     You can use the EIN for the state ID - the military EIN is 35-9990000.