Tressa McClurg descends from Joseph & Mary (Henry) McClurg who settled in Mercer Co. PA prior 1800. Joseph McClurg came to America from the North of Ireland, met and married Mary Henry in Westmoreland Co. PA. Parents of Joseph McClurg were David & Ann (Pollock) McClurg of Limavada, Ireland at Templemoyle.
One of Joseph's sons, Daniel McClain McClurg is the father of the William A. McClurg you speak about and who is the father of Tressa McClurg. In order to eliminate searching for a McClain tie, In his 1822 letter back home to Parents, Joseph told him he had named a son after the Rev. McClain who was also known to parents and presently living in Mercer Co. PA.
I also list a sister Hazel in that family of William A. McClurg, but have no date of birth for her.
Hope this information assists in tracing your lineage.