The 1900 census shows Tressie J. McClurg, born Jan 1887, as the daughter of William A. McClurg, born April 1860, living in Crawford County, PA. Also listed is son W. Leroy, born March 1889. His wife Elizabeth was not the mother of Tressie. The 1910 census shows William with his third wife Mary.
William Leroy McClurg's World War I and II draft cards show he was born March 14, 1889 in Sheakleyville which is in Mercer County, PA. The Social Security Death Index has a William McClurg who was born on the same day and died in Sept 1979, coincidently in Andover, OH.
Some of these records you can look at for free at labs.familysearch.org and Ancestry.com. For those you cannot see for free I suggest checking with your local libraries to see if they have Ancestry or Heritage Quest.
I suggest getting Tressa and William's Ohio death certificates and obituaries which will help to confirm this information and should give you their mother's name. As for William Sr. I suggest contacting the Crawford County Historical Society and the Genealogical Society. The Meadville Family History Center may be able to help you too. There are also other steps you can take if you are interested.