Map of Japanese provinces (1868) with Mikawa Province highlighted
Mikawa Province (三河国 Mikawa no kuni) was an old province of Japan in the area of Aichi Prefecture on the island of Honshū. It was also known as Sanshū (三州 or 参州).
Mikawa had borders with Owari, Mino, Shinano, and Tōtōmi Provinces.
View of Mikawa Province, woodblock print
In the Edo period, the Tōkaidō road was the main route between the Imperial capital at Kyoto and the main city of the Tokugawa Shogunate. The road passed through Mikawa.
In the Meiji period, the provinces of Japan were converted into prefectures. The maps of Japan and Mikawa Province were reformed in the 1870s.
Toga jinja was the chief Shinto shrine (ichinomiya) of Mikawa. 
Media related to Mikawa Province at Wikimedia Commons