Its territory was located in present-day northern Anhui and northwestern Jiangsu, as well as part of Shandong and Henan.
Pei was established in early Western Han on an area formerly known as Sishui Commandery (泗水郡) during the Qin dynasty, and received its name from Pei County, Liu Bang's home county.
In 2 AD, the commandery consisted of 37 counties: Xiang (相), Longkang (龍亢), Zhu (竹), Guyang (穀陽), Xiao (蕭), Xiang (向), Zhi (銍), Guangqi (廣戚), Xiacai (下蔡), Feng (豐), Dan (鄲), Qiao (譙), Qi (蘄), Zhuan (颛), Zheyu (輒與), Shansang (山桑), Gongqiu (公丘), Fuli (符離), Jingqiu (敬丘), Xiaqiu (夏丘), Xiao (洨), Pei, Mang (芒), Jiancheng (建成), Chengfu (城父), Jianping (建平), Cuo (酇), Li (栗), Fuyang (扶陽), Gao (高), Gaochai (高柴), Piaoyang (漂陽), Ping'e (平阿), Dongxiang (東鄉), Lindu (臨都), Yicheng (義成) and Qixiang (祈鄉).
[1] During Eastern Han, the commandery was converted to a principality nominally held by an imperial prince.
A number of counties were merged in early Eastern Han, and in 140 AD, the principality administered 21 counties, including Xiang (相), Xiao, Pei, Feng, Guyang, Qiao, Xiao, Qi, Zhi, Dan, Jianping, Linsui (臨睢), Zhuyi (竹邑), Gongqiu, Longkang, Xiang (向), Fuli, Hong (虹), Taiqiu (太丘) and Zhuqiu (杼秋).