From 1910 census 6th Ward Y'town Mahoning County OH: John K. Cahill age 39 born PA.Wife Sarah age 54, married twice and daughter Rita age 13.
From 1900 census: 6th Ward, West Federal Street, Youngstown, OH.John, a puddlers helper, age 30, born PA in Sept of 1870. Also shown in this census were Sarah, a son Earl born July 1894 and Rita born July 1895. Plus a step daughter named Lizzie Morgan and step sons William and Thomas. The most likely match for parents show up in the 1870 census of Allegheny County Pennsylvania (prior to birth of your John) It shows John Cahill age 27 born Canada and wife Kate age 26 born Ireland. Listed with them were children Ellen and Patrick. (your John's elder siblings) Hope this helps.