In the broadest sense, when we talk about the Cree dialects, there's a division between western and eastern Cree dialects, which run more or less along the Ontario-Quebec border, although Atikamekw in Quebec is usually considered one of the western dialects because of a particular sound change.
Broadly speaking, we talk about five dialects in the west: Plains, Woods, and Swampy, which can be subdivided, with Moose Cree along the southern coast of James Bay, Moose Factory, and so on, and Atikamekw in Quebec. There are the eastern Cree dialects, Innu, which has subdialects as well, Naskapi, and East Cree, with northern and southern East Cree.
Those are the main dialects.