Final answer:
The first all-female college founded by Emma Willard was the Troy Female Seminary, which became known as the Emma Willard School.
Step-by-step explanation:
The first all-female college opened by Emma Willard was the Troy Female Seminary, later known as the Emma Willard School. This institution was a significant advancement in female education during the antebellum period and was crucial in educating future leaders of the women's rights movement, including notable figures such as Elizabeth Cady Stanton. Despite early challenges, Willard's vision was realized in 1821 when sufficient private contributions allowed for the establishment of her school, marking an important milestone in the education reform movement spearheaded by figures like Horace Mann and William Holmes McGuffey.