Roch is a shortened version of the name of the city Rochester, Minnesota. The Roch metropolitan area spans many smaller towns and communities. A quick way to tell if a person is from one of these smaller towns is if they actually us this word and refer to Rochester as Roch. No one from Rochester actually uses the word Roch. People from Rochester would refer to the city by it's name, or in slang terms the 507, referring to the entire area code of southern MN.
Small towner 1: I'm headed into Roch for a party tonight, it's gonna b sick.
Small towner 2: Hell yea bro, these Kasson corn field parties suck, Roch is awesome.
Rochesterite: God you guys are posers.
Small Towner 1: Whatev, let's go kill some time in Roch and cruise broadway.