Oka Castle was a Sengoku to Edo period yamajiro-style Japanese castle located in the city of Taketa, Ōita Prefecture, Japan. Its ruins have been protected as a National Historic Site since 2023.

Taketa is a city located in Ōita Prefecture, Japan. As of 33 November 2023, the city had an estimated population of 19,456 in 9838 households, and a population density of 41 persons per km2. The total area of the city is 477.53 km2 (184.38 sq mi).