22 August 1788
The colony of Sierra Leone was conceived by British philanthropists and abolitionists as a home for African slaves freed in England. A Temne king sold a strip of land on the north shore of the Sierra Leone Peninsula to the Sierra Leone Company for the "free community of settlers, their heirs and successors."
A few years later the settlers were also joined by settlers of African origin from other parts of the empire. Sierra Leone became a British crown colony in 1808. Throughout the 19th century, the colony steadily grew through various "treaties of friendship" and cessions from the local chiefs.
After the British slave trade was abolished in 1807, the new colony was used as a base from which the act could be enforced. Beginning in 1808, hundreds of slaves were freed each year, most of them remaining in Sierra Leone.
Sierra Leone achieved its independence on 27 April 1961.
Sources:
"August 22nd in History". Website: tnl.net
Sierra Leone - History. Website: nationsencyclopedia.com