I work in Maryland, but my company is headquartered in Delaware (and the Delaware address is on my W2). Do I put down that I work in Maryland or Delaware?

[TerryA]

It doesn't matter where the employer "headquarters" is located. What matters is in which state did you work? Sound like you work in Maryland so Maryland gets to tax your W-2 income. If you live in MD as well then that's the only state return you probably need.