This butterfly has forewing markings seem somewhat like a hybrid between an Eastern Tiger Swallowtail (Papilio glaucus) and a Canadian Tiger Swallowtail (Papilio canadensis). Extrapolation of its size based on a typical size of 3" for a Common Milkweed flower head results in a wingspan of over 4". Given its similarity to Butterfly #1, I wonder if it might instead be an Appalachian Tiger Swallowtail (Papilio appalachiensis).

Taken near the Water Towers at Prospect Park in Shrewsbury, Massachusetts on 8-July-2017. The location is the highest point in Shrewsbury (761 feet).