Yamaguchi Tadasada (Japanese: 山口 正定) (October 18, 1843 – March 21, 1902) was an Imperial Japanese Navy veteran of the Boshin War and Meiji-era Japanese politician. He was the second governor of Ibaraki Prefecture (1872). He was Grand Chamberlain of Japan (1878–1884). He was a recipient of the Order of the Sacred Treasure (3rd class, 1888; 1st class, 1902)[1][2] and the Order of the Rising Sun (2nd class, 1895).[3]