Little is known about this branch of the Dunder Mifflin Paper Company. In a deleted scene from Branch Wars, Michael lists a specific characteristic of each branch, explaining that "Yonkers has the 2 hot girls."
A file on Stanley’s desk in S4: E3 reads dm-Yonkers_letter
In the episode, Survivor Man, Toby mentions that a man named Mark Chisholm attended Ryan's wilderness retreat, indicating that Chisholm is a regional manager. It is possible that he is the regional manager of the Yonkers branch, though he could be the regional manager for Rochester, Nashua, Akron, or Camden.