Castlereagh Upper (named after the former barony of Castlereagh) is a historic barony in County Down, Northern Ireland.

[2] It was created by 1841 with the division of Castlereagh into two.

[3] It is bordered by eight other baronies: Castlereagh Lower and Dufferin to the east; Lecale Lower and Kinelarty to the south; Iveagh Lower, Lower Half, Iveagh Lower, Upper Half, and Massereene Upper to the west; and Belfast Upper to the north.

[2] Below is a list of settlements in Castlereagh Upper:[4] Below is a list of civil parishes in Castlereagh Upper:[4][5][6]