白河藩
At the age of 17, he was adopted by Matsudaira Sadakuni, the "daimyō" of Shirakawa Domain in Mutsu Province, over the objections of the Tayasu clan, which was thus left without an heir. This issue arose the following year, and although Sadanobu petitioned to be reinstated with the Tayasu clan, Shogun Ieshige, at the instigation of Tanuma Okitsugu refused, and the clan remained without a leader for over a decade. In the meantime, Sadanobu succeeded to the head of the 100,000 "koku" Shirakawa Domain in late 1783 following his stepfather's protracted illness. He was immediately faced with his domain's economically disastrous position: of 110,000 "koku" that it was supposed to be able to produce, 108,600 had been reported "lost". Sadanobu worked ceaselessly to fix the economic situation in Shirakawa, finally saving it and bringing its finances and agriculture back to stability.