With roots in the First Day Society (founded 1790), the InFaith officially formed in 1817 as the "Sunday and Adult School Union".

Several people influential in the United States during the 19th century, including Francis Scott Key, Associate Supreme Court Justice Bushrod Washington, and U.S. Mint Director James Pollock, served as officers of the mission; many others supported the mission in other ways.

Eventually, the ASSU grew beyond starting Sunday schools to include church planting, Christian camping, and other ministries.

Under this name, the mission continued to start new evangelical works in overlooked communities across the United States.

While InFaith has grown well beyond its original goal of starting Sunday schools for poor children, the mission faithfully continues to convey the unchanging truth of God’s Word to a changing culture.