The kingdom was founded by the Temne ethnic group in or around 1505 by migrants from the north, seeking trade with the coastal Portuguese in the south.
Under Nembanga's reign (1775–1793), the Koya kingdom signed a treaty, which made it possible for the establishment of a British colony on the peninsula of Sierra Leone in 1788.
Koya participated in the trans-atlantic slave trade, though sources state that such commerce was much more privatized than in other kingdoms.
Koya lost the northern shoreline of Sierra Leone to the British and Port Loko to the Susu.
The kingdom became a British protectorate on 31 August 1896 after which the Koya kings lost virtually all power.