LBJ and Hoover were born and raised at these places, at least for part of their youth.
If you're just born somewhere and immediately left, it won't matter unless that place is verysmall and obscure.
Correction: LBJ was actually raised in neighboring Blanco County.
The Johnson name is gold in both counties
The county town of Blanco is called Johnson City, so I guess that dates back to before LBJ.
Johnson City is named after an ancester of LBJ's... pretty much the only way a Democrat can win in that part of Texas is to have the surname "Johnson".