Kajō Park, Urban park in Yamagata, Japan

Kajō Park is a 35.9-hectare urban park on the site of Yamagata Castle, a nationally designated historic site in central Yamagata. Its roughly 500-metre-square outline, visible even from satellite images, is formed by the moats and stone walls of the castle's second enclosure. The park holds the Yamagata Prefectural Museum and the former Saiseikan hospital building, now the city museum, and its cherry trees along the stone walls are lit up in spring.

A fortress was founded here in 1356, and then rebuilt and expanded by a regional lord between 1592 and 1614. That period of rebuilding shaped the layout and structures that remain visible today.

The park's name comes from Kajō (Kasumi-ga-jō), an old alias of Yamagata Castle. Inside the grounds stand the Yamagata Prefectural Museum and the Yamagata City Museum, housed in the former Saiseikan hospital building, a nationally designated Important Cultural Property moved here. In spring the cherry trees along the stone walls are lit up and reflected in the moat, and trains on the Ōu Main Line slow down as they pass the park.

The park is a stop on Yamagata's trolley bus route, and Yamagata Station is the nearest railway station. The reconstructed East Otemon gate and the Korai-mon gate with its earthen walls are open to the public. The city plans to finish excavating the honmaru and restore its north masugata enclosure by 2033.

The name Kajō, also rendered Kasumigajō, comes from Yamagata Castle's nickname and was later given to the park. The grounds cover about 35.9 hectares of the former castle site, an outline still visible in satellite images of the city.