Fa Zheng's ancestral home was in Mei County (郿縣), Youfufeng Commandery (右扶風郡), which is in present-day Mei County, Shaanxi.
Fa Zheng's great-grandfather, Fa Xiong, served as the Administrator (太守) of Nan Commandery (南郡; around present-day Jingzhou, Hubei) during the reign of Emperor An in the Eastern Han dynasty.