The castle originally established by Shiba Kaneyori at Yamagata is said to have been about the size of the honmaru of the later Yamagata castle. Shiba later took the name of the surrounding area and changed his name to Mogami. Mogami's ancestor Mogami Yoshiaki reconstructed the castle into a much larger fortres in 1592. He added the ninomaru and sannomaru, but there was never a large tenshukaku (donjon) that you see at other castles. It did however have three 2 story and one 3 story yagura.

While Mogami Yoshiaki went to the Battle of Sekigahara with Tokugawa Ieyasu, it is said that Uesugi Kagekatsu's general Naoe Kanetsugu went to attack Yamagata Castle but he could find it as it was buried in thick fog. Thereafter, the castle was also known as kasumigajo, the castle in the haze.

At his peak after the battle of Sekigahara Yoshiaki controlled land yielding 570,000 koku. Yoshiaki died in 1614 and his successor Iechika died shortly thereafter in 1617. His sucessor Yoshitoshi was reduced to 300,000 koku and later moved to Mikawa. Over time the importance of Yamagata Castle to the Tokugawa rule over Eastern Japan declined, and with it the size of territory controlled by the lord of Yamagat Castle was also reduced.

Yamagata Castle is well known today for the authentic wooden econstruction of the East Gate. As you can see from the above picture, this is a masugata style gate. The 2 tamon yagura, high stone walled moat, and the walls surrounding the top make it most impregnable.