Satyrium favonius ontario: (W. H. Edwards) (Lepidoptera: Lycaenidae) is considered to be a rare butterfly in the northeastern United States. It receives legal protection in the state of Massachusetts as a Species of Special Concern. We studied the ecology and natural history of a colony of S. f. ontario at Great Blue Hills Reservation in Canton, Massachusetts. In addition, we assembled a database of confirmed S. f. ontario occurrences (n = 362) and used this along with climate and oak abundance data to build a species distribution model for the northeastern portion of the butterfly’s range in the United States. The model predicts that essentially the entirety of southern New England is suitable for the species, and thus its modeled distribution extends well north of all documented colonies/localities. Just two climate variables, precipitation seasonality and minimum temperature of the coldest month, explained 95% of the model and largely determined relative suitability predictions. We make the case that the hairstreak is a canopy-dwelling insect that sporadically makes ground-level visits, and that its assumed regional rarity is due to detection difficulties rather than demographic rarity. While the butterfly may be imperiled and worthy of legal protection in portions of its range, we question the validity of population estimates and necessity of conservation efforts based on ground-level adult sightings, and recommend larval sampling using burlap bands as a more reliable method to census this butterfly. We also discuss the possibility that other Satyrium and more distantly related hairstreaks (e.g., Callophrys hesseli and Parrhasius m-album) may be additional examples of temperate, canopy-based butterflies.