Sierra Leone was a country in Africa.
In 1754, the Doctor's TARDIS materialised on a slave ship off the coast of Sierra Leone, where the Seventh Doctor found Kadiatu Lethbridge-Stewart. Having arrived here from 1871 Paris through a time rift, Kadiatu had slaughtered the entire crew, her genetic programming having placed her in killing mode the moment she felt threatened by them. The Doctor took her to the People for observation. (PROSE: The Also People)
Lt Alistair Gordon Lethbridge-Stewart was stationed in Sierra Leone some time in the 1950s, where he met and fathered a son, Mariama, with Mariatu, eldest daughter of Chief Yembe of the Rokoye village. (PROSE: Transit)
In the 21st century, Sierra Leone had a football team who were due to face the Ghana Black Stars for the Africa Cup of Nations, but their match was at least postponed by a sudden global afforestation which the Twelfth Doctor and Coal Hill School kids under the care of Clara Oswald and Danny Pink witnessed. (TV: In the Forest of the Night)