The area of Tamba-Sasayama was part of ancient
Tanba Province, and corresponds almost exactly with ancient Taki District. Sasayama developed as a
castle town around
Sasayama Castle, which was constructed in the early
Edo Period. The town of Sasayama was established on April 1, 1889, with the creation of the modern municipalities system, and expanded its borders through municipal mergers with neighboring villages in 1955 and 1975. It was raised to city status on April 1, 1999, from the merger of the former town of
Sasayama, absorbing the towns of
Konda,
Nishiki and
Tannan (all from Taki District). On November 18, 2018, the city held a successful referendum on changing its name from Sasayama to Tamba-Sasayama in reference to the historical
Tanba Province, which still has some influence on local branding and politics. The referendum about changing a municipality's name is the first of its kind in Japan, and the new name officially came into effect in May 2019. ==Government==