John W. Rigdon's biography of Sidney Rigdon reports that he began preaching in Pittsburg in 1819.
John Wickliff, "Life story of Sidney Rigdon," MS 3451, Church History Library
After his [father's] death he continued on the farm with his mother until he was twenty six years old. In that year he united with the church called at that time the Regular Baptest... He left the farm and went to [unreadable] with the Rev Andrew Clark a minister of the same faith at Pittsburgh P.A. It was during his continuance with him he procured a license to preach and he preached his first sermon at Pittsburgh at the age of twenty seven and he continued to preach the gospel from that time adopting it as his profession. This was in the month of March 1819.