The province of Kii occupied the south of the Kii Peninsula (current departments of Wakayama and part of Mie). From ancient times, this mountainous province emerged a place of legends transmitted through ancient chronicles. In the Heian period, many Buddhist monasteries were established in the region, such as Kongōbu-ji on Mount Kōya, the headquarters of the Shingon school, Kogawa-dera, and later Negoro-ji. The Kumano shrine (Kumano-jinja) which was, and still is, one of the most famous in the country, is also located in Kii. The pilgrimage to Kumano was one of the most frequented in the Middle Ages, and several emperors traveled there from the capital through the mountains of the Kii Peninsula.
At the end of the 14th century, the province was the scene of a succession conflict within the Yamana family. This forced the shogunate to intervene militarily in 1394 (Meitoku no ran). Kii eventually came under the direction of the Hatakeyama; however, in the 16th century part of the territory fell outside the control of the great feudal lords with the establishment of autonomous organizations, such as the Saika-shū in the region of the Wakayama estuary, or the independent warrior monks of Negoro-ji. Hideyoshi attacked and destroyed these organizations in a military campaign in 1585. The province was then entrusted to his younger brother Hidenaga, who already held Yamato. After the siege of Osaka Castle in 1614–1615, the province was entrusted to a son of Tokugawa Ieyasu, the founder of the Kii branch of the Tokugawa.