She was the youngest of ten children, and inherited the intellectual and moral qualities of a long line of Puritan ancestry.

About 1789, her grandparents removed with their families from Lyme, Connecticut, to Otsego County, New York, at that time a wilderness, and settled in the neighborhood of what is now Burlington.

[1][3] Her mother (died 1860), eldest daughter of Judge Peck, was a good scholar in her day, especially in mathematics.

She was left by the death of her husband with the care of nine children -one having previously died- six sons and three daughters, of whom Anna was the youngest.

It was a daily walk through summer's heat and winter's cold, over steep hills and through valleys and plains 1 mile (1.6 km) away to the school-house.

There, she was drilled in Webster's Spelling Book, Morse's Geography and Murray's Grammar, which she committed from beginning to end with no thought of its value, or scarcely of its meaning.

[3] She left Burlington in the fall of 1836, when about 20 years of age, and taught a district school at Barre, New York in the neighborhood of Albion, New York for about seven months, devoting the intervals of her school hours to other employments, such as spinning and weaving, to eke out the slender wages she received of US$2 per week, and obtain the means of support and further education.

"[3] Not receiving any favorable reply, she went alone and almost unfriended, to Warsaw, New York, and there, after many discouragements, succeeded in opening a Seminary for young ladies, October 2, 1843.

While here, she had many applications to go elsewhere; one to take charge of the Seminary at Albion, and also to go as Principal at Le Roy, New York, but she decided to remain in Oakfield another year.

The diversity in the sphere of life and employment opportunities for each seemed at that time to require a somewhat different curriculum of study and method of training, for which separate institutions were demanded.

Accordingly, they resolved after a series of conventions, representing especially the Congregational and Presbyterian ministers and churches of the Northwest, to establish a college at Beloit, Wisconsin, and a Seminary in Northern Illinois.

[3] Friends of the enterprise in Rockford, who had heard of Sill's success and reputation as a teacher, prominent among whom was the Rev.

L. H. Loss, then pastor of the Congregational Church, wrote to her concerning the new enterprise and invited her to come to Rockford and open a school for young ladies as preparatory to the future Seminary.

School commenced on July 11, opening with 53 scholars, and the following day, there were 60,[3] holding recitations in the city's old courthouse building.

Sill opened a modest boarding-house, and with the funds earned, improved the schoolroom, bought the books needed, placed curtains in the windows, and prevailed upon the students to supply desks.

[3] The immediate and large success of the school, which soon outgrew its accommodations, demonstrated the felt need and demand for higher female education in the growing West, and it was very soon recognized as the beginning of the Rockford Seminary.

With this, the foundation of another building was laid, but erected slowly with borrowed money to complete it, the debt being secured by mortgage on the property.

Appeals were sent out to friends of Christian education, and Sill again visited New England and secured funds for the completion of another building, a chapel with connecting wings.

During these years, while responsible for the business issues of the institution, she not only continued the personal instruction of her classes, and superintended the management of the school, but she took an active and often a leading part in the social and religious life of the community, attending regularly the prayer meetings and other meetings of the Church, teaching a Bible-class in the Sunday School, mingling in social circles and contributing her personal influence as appropriate.