[1][2] Adrian's paternal great-grandfather, Belain Posey (1737-1791),[3] served as a captain in Colonel Thomas Ewing's Third Battalion of the Flying Camp during the Revolutionary War.
[8] It was during this period that Posey emerged as an ardent supporter and the instrumental, driving force behind moving the county seat from Port Tobacco to La Plata.
In one writer's estimation, Adrian Posey was "the dynamic arch-enemy of old Port Tobaccoites and the ever vigilant, forceful, enthused supporter of anything having to do with La Plata's county pre-eminence in politics, commerce, and general economic well-being.
[14] Adrian and his wife Mary Agnes "Mamie" Howard Posey, who were married January 29, 1885,[15] built their Victorian style home, The Maples, in downtown La Plata[16] and raised one son and three daughters.
[19] Posey died of heart disease on July 2, 1922, at The Maples in La Plata and was laid to rest in the cemetery adjacent to historic St. Thomas Manor.