William L. Overman b. abt 1835

I am looking for the parents of William L. Overman born abt. 1835 in Highland County Ohio.He is listed on the 1850 census living with Susannah Overman Fletcher in Muscatine County, Iowa.I am not sure if she is his sister or a cousin, but he was only 15yrs old at the time of the census, and she was not old enough to be his mother, she was born in 1827.I am wondering of his/their parents died early and that is why he is with her?When William enlisted in the Civil War, he listed Highland county Ohio as his birthplace.Other than that, the only other proof I have that they were from Ohio is that on the 1850 census, both William and Susannah list Ohio as their birthplace.I have found no records in Ohio that puts them there. In the census, an 11 yr old boy by the name of James Kennedy was also living with them, also born in Ohio.I am guessing back in Ohio, the Kennedy and Overman families are somehow connected, and that may be the clue to finding William's parents.