Sayō is located in ancient Harima Province, and the name appears in the Heian period Engishiki records.

From the Kamakura period Hirafuku-juku prospered as a post town on the Inaba Kaidō, the main highway from Kyoto and Osaka to Inaba Province in western Japan, and in the Nanboku-chō period, the Akamatsu clan built Rikan Castle overlooking the town.

In August 2009, around a dozen people in Sayo are dead or missing as a result of flash floods due to Tropical Storm Etau, according to NHK.

Sayō has a mayor-council form of government with a directly elected mayor and a unicameral town council of 14 members.

In terms of national politics, the town is part of Hyōgo 12th district of the lower house of the Diet of Japan.