I lived with my mom in MD before I joined the Army. She sold the house and doesn't have a permanent residence at the moment. Does that mean I file KY state taxes or MD?

If you want to keep Maryland as your domicile- resident state you can do so while you are active duty orders.  You can use your KY address for mail only but not your state of residence.  If you change your domicile to Kentucky, you may not be able to change it until you establish a new domicile by moving.

So I have to keep MD as my "domicile-resident state" even if I don't have a current address there? Do I just put my old address?

You do not have to, but unless you want Kentucky to be your resident state even if you PCS I would keep it MD.  If you mean for your taxes, I would use your current KY address- as your mailing address.  If you only have your military pay, you do not have to file a KY return so when you get to the states be sure to delete it before you have to file and add MD instead.

I'm not deployed right now. I'm stationed in Ft Campbell KY. I only say that bc you said "so when you get to the states be sure to delete it before you have to file and add MD instead." I'm not sure what you mean by that. Whenever I return to MD? Also does the mailing address I enter for my taxes really even matter if the money from my tax return is going straight to my bank account?

Oh, if you are still in training I definitely would NOT change domicile to Kentucky.  When you are in the military (active duty) you can keep your state of residence when you enlisted, and so you file and pay tax to that state and not in the state you are at.  It keeps some consistency if you get moved a lot.  If you put the KY address in Turbo Tax, it adds KY as state to file- and you are correct it is not as important if you are direct deposit but if the IRS needs to contact you for any reason, they mail first so you want to have a current address on file with them.

Alright thank you for your help 🙂

You are welcome and I wish you the best in your service.