Cousins Beach, as depicted in "The Summer I Turned Pretty," is a fictional beach town believed to be located in Massachusetts, likely inspired by Cape Cod and near Boston. The distance from Boston to the area generally considered as Cousins Beach is about 120 to 121 miles by road. This fictional location is implied to be a Cape Cod-esque Massachusetts beach town south of Boston.

Therefore, the approximate driving distance from Boston to Cousins Beach would be around 120 miles.