The Mourning Warbler breeds from southeast Yukon and northeast British Columbia across to Newfoundland and down into the northern tier of states from Minnesota to Maine. The species winters from Nicaragua into Colombia, Venezuela, and Ecuador. The Mourning Warbler is a rare migrant through Montana with fewer than seven observations reported in a typical year (Pitocchelli 2019,, MTNHP 2019).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.