Born in Middletown, New York, Knapp moved with his parents to Illinois in 1839 and settled in the city of Jerseyville.

Knapp was elected as a Democrat to the Thirty-seventh Congress to fill the vacancy caused by the resignation of John A. McClernand.

[1] In 1847, at age nineteen, Knapp had served as a private secretary to Governor Augustus French, a Democrat.

[6] One modern writer states, "compared to [his predecessor] McClernand, Knapp sounded too concerned with opposing President Lincoln and less committed to the war effort.

This article incorporates public domain material from the Biographical Directory of the United States Congress