Numazu Castle (沼津城 Numazu-jō) was a Japanese castle located in the city of Numazu, Shizuoka Prefecture, Japan. It was a hirayama-jō, a castle built on a plains rather than a hill or mountain. During the Edo period, Numazu castle was home to the Mizuno clan, daimyō of Numazu Domain.
In April 1777, when the former wakadoshiyori Mizuno Tadatomo was transferred from Ohama Domain in Mikawa province to Numazu, he was assigned revenues of 20,000 koku and authorized to build a castle. The site he chose was the ruins of Sanmaibashi Castle (三枚橋城), a Sengoku period fortification which had been erected by Takeda Katsuyori in 1579, and destroyed in 1614, when the Numazu area became a tenryō territory after the death of Ōkubo Tadasuke. The castle consisted of three concentric moats forming three baileys. The keep was a three-story structure.
Numazu prospered in the Edo period as Numazu-juku on the Tōkaidō, and eight generations of the Mizuno clan resided at Numazu castle, with their revenues eventually rising to 50,000 koku.
After the Meiji Restoration, Numazu Domain was abolished with the creation of Shizuoka Domain for the retired ex-Shōgun Tokugawa Yoshinobu in July 1868. However, in 1873, the Meiji government ordering the dismantling of all castles and fortifications in Japan. Numazu castle was destroyed, its moats filled in, and its land sold to private holders.