Genealogy research is a fascinating rabbit hole and there are a lot of sites like Ancestry that make it a lot easier.
I found out that my great great grandfather was in the Civil War and a pioneer who founded a town, because of that he was well known enough at the time there was biographical information that mentioned that he adopted a daughter. So my great grandmother was adopted and he wasn't really my great great grandfather by blood. When I mentioned this "discovery" to my dad, he said that they knew she was adopted because of something they found written in a family Bible that had been passed down. The historical biographical information gave it some context even though it didn't give any insight as to who her biological parents were.
I found out that my great great grandfather was in the Civil War and a pioneer who founded a town, because of that he was well known enough at the time there was biographical information that mentioned that he adopted a daughter. So my great grandmother was adopted and he wasn't really my great great grandfather by blood. When I mentioned this "discovery" to my dad, he said that they knew she was adopted because of something they found written in a family Bible that had been passed down. The historical biographical information gave it some context even though it didn't give any insight as to who her biological parents were.