The prior two commenters did not answer the question. If you work in New York but live in New Jersey, the IT-2104 should be all you need, because you have no earned income in New Jersey, so there should be no reason to complete an NJ-W4. There is one caveat however - if you are going to spend a significant of WORKING days in New Jersey and your employer actually tracks this and withholds New Jersey income tax, then you should complete an NJ-W4 so not too much New Jersey tax is withheld. Otherwise there is no reason to complete an NJ-W4.