Sierra Leone is located on the west coast of Africa, between the 7th and 10th parallels north of the equator. Sierra Leone is bordered by Guinea to the north and northeast, Liberia to the south and southeast, and the Atlantic Ocean to the west. The country has a total area of 71,740 square kilometers (27,699 square miles), divided into a land area of 71,620 square kilometers and water of 120 square kilometers. The country has four distinct geographical regions. In eastern Sierra Leone is an interior region of large plateaus interspersed with high mountains, where Mount Bintumani reaches 1,948 meters (6,390 ft), the highest point in the country. The upper part of the drainage basin of the Moa River is located in the south of the region.

In the central part of the country is a region of lowland plains, containing forests, bush and farmland, that occupies about 43% of Sierra Leone's land area. Starting in the west, Sierra Leone has some 400 kilometres (250 miles) of coastline, giving it both bountiful marine resources and attractive tourist potential. This is followed by low-lying mangrove swamps, rain-forested plains and farmland. The national capital Freetown sits on a coastal peninsula, situated next to the Sierra Leone Harbor, the world's third largest natural harbour. The climate is tropical, with two seasons determining the agricultural cycle: the rainy season from May to November, and a dry season from December to May, which includes harmattan, when cool, dry winds blow in off the Sahara Desert and the night-time temperature can be as low as 16 °C (60.8 °F). The average temperature is 26 °C (78.8 °F) and varies from around 26 °C (80 °F) to 36 °C (90 °F) during the year.

Environment
Logging, mining, slash and burn, and deforestation for land conversion - such as cattle grazing - have dramatically diminished forested land in Sierra Leone since the 1980s. Correspondingly the habitat for the African Wild Dog, Lycaon pictus, has been decreased, such that this canid is deemed to have been extirpated in Sierra Leone.

Until 2002, Sierra Leone lacked a forest management system due to a brutal civil war that caused tens of thousands of deaths. Deforestation rates have increased 7.3% since the end of the civil war. On paper, 55 protected areas covered 4.5% of Sierra Leone as of 2003. The country has 2,090 known species of higher plants, 147 mammals, 626 birds, 67 reptiles, 35 amphibians, and 99 fish species.

In June 2005, the Royal Society for the Protection of Birds (RSPB) and Bird Life International agreed to support a conservation-sustainable development project in the Gola Forest in southeastern Sierra Leone, an important surviving fragment of rainforest in Sierra Leone.