I have a valid US visa, I will be going to northern Cyprus.
Will having the Turkish e-visa allow me to enter Northern Cyprus?
Both Turkey and North Cyprus consider the other to be fully independent countries so travel requirements for one are not relevant to the other. The visa requirements for North Cyprus are outlined here. There are only 3 countries which require visas to enter, all of which require in-person applications. In short, US or Turkish Visas are not relevant for entry into Northern Cyprus.