I've also discovered, as more close matches appeared, that there are genetic links between this massive group of Willis family members and Aida and my closest mystery cousin, the one who self-identifies as Cherokee but turned out to be 100% white lady. All my mystery people are turning out to reside on the same mysterious branch of my family tree. I guess this shouldn't surprise me since I have so many matches across most of the rest of my tree that I can often tell how I'm related to someone based solely on shared DNA matches. (I have a LOT of matches. I credit it to being so historically American and the DNA testing companies also being American.)
There is so much data it's hard to compile into one place where I can see it at a glance. Today I started to draw the family tree on a wall-sized dry erase surface in the hopes of fitting all the DNA matches I know and then trying out places where my mystery cousins might fit. It makes me look like a conspiracy theorist, or so I like to think. I just need some red string and photographs.
I currently have one most likely suspect for the role of gg-grandfather based on proximity of DNA matches, though he isn't necessarily it. My next step will be to figure out some currently living descendants who might someday DNA test and to hypothesize what their matches to other cousins should look like. I think the match I'd most like to see would be one of my g-grandmother's descendants, any of whom should match to my entire mystery bunch as well as to the descendants of my gg-grandmother's clan in Illinois.
Something to consider for anyone who thinks they can keep a child's paternity a secret if they just wait out the clock: the person I'm in the process of finding out isn't biologically my ancestor is 150 years my senior. He died decades before my parents were born. He fought in the Civil War.
DNA testing is still in its infancy. Who knows what DNA tests will be able to unearth in another 150 years.
If anyone has done genetic genealogy focusing on people this far removed from the current era and has advice or suggestions for what I should be doing next, please let me know. It's hard since the margin of error increases -- snowballs, really -- each time you go back another generation.