Beornings were Woodmen in the Vales of Anduin between Mirkwood and the Great River. They were not friendly to the outsiders but hated the Orcs and Wargs and they defended the Ford of Carrock and the High Pass in return for tolls.
The Beornings as the Woodmen, are akin to the Third House of the First Age. It's possible that the Beornings first dwelt in the Misty Mountains until driven out by the Orcs, thus explaining their hatred.
It is not clear if the Beornings were descendants of Beorn, or if Beorn was just one of them.
Also, it is never mentioned if they retained Beorn's ability to take the shape of a bear.[source?]