Wiley Dunham was born on Tuesday, January 30, 1877, in Piketon, Ohio. Dunham was 25 years old when he broke into the big leagues on May 24, 1902, with the St. Louis Cardinals.
Charlie Starr was born on Friday, August 30, 1878, in Pike County, Ohio. Starr was 26 years old when he broke into the big leagues on April 29, 1905, with the St. Louis Browns.
Branch Rickey, I have found several places where he was supposed to be born in Stockdale, Ohio and Flat, Ohio. I dont know where Flat is, but Stockdale is on the Pike/Scioto border, but it is officially in Pike County
These 3 players are the only paid professional players from Pike County that I can find. They all three played for the St. Louis Cardinals or Browns.
Others from Pike county have made it to either farm teams or lower levels of professional sports, but these 3 are the only I can find that actually made it to the highest level of professional sports.
All of these can be verified on baseball almanac.