Genealogy / What does my Polish name mean? [400]

[Moved from]: Dorohusk, Derkacz, Derkez - My great grandfather came from Poland

Hi everyone, I'm new here. I looked for a place to introduce myself but couldn't find one. Sorry if I'm upsetting others by straight off asking questions. My grandfather came to the US before WWI from Poland. Not much was know of him as he even changed his last name as he couldn't speak English and they spelled the last name the way he pronounced it. My question is I recently acquired some papers about him during WW1. Is says he was born in Dorogust, Russia. We know he spoke Poland and Russia occupied Poland when he came here, but there's nothing that I can find about anything to do with a town called Dorogust. Does anyone might know anything bout this? It would be most helpful. We also know he would have been born Jan Derkacz in Poland but in the US was called John Derkez. Again thank you in advance for any help anyone might have.