Koyu (児湯郡, Koyu-gun) is a district in Miyazaki Prefecture, Japan.

As of October 1, 2019, the district has an estimated population of 68,269 and the density of 95.5 persons per km². The total area is 715.03 km².

• Kawaminami
• Kijō
• Shintomi
• Takanabe
• Tsuno
• Nishimera

32°14′56″N 131°28′59″E / 32.249°N 131.483°E / 32.249; 131.483