You will need to file a Non-Resident Delaware return and a Resident Pennsylvania return.
The U.S. Supreme Court ruled against double taxation in 2015,
stating that two or more states are no longer permitted to tax the same
earnings. So, if you live in Pennsylvania but work in Delaware and pay taxes on
that income in Delaware, Pennsylvania cannot tax you on it as well. Pennsylvania must offer you a credit for taxes you paid elsewhere.
So you won't pay taxes on the some money twice. You'll have to
spend a little more time preparing multiple state returns, however.
