The United States established diplomatic relations with Sierra Leone in 1961, following its independence from the United Kingdom. U.S.-Sierra Leone relations are cordial. About two percent of Sierra Leone's population are Krio, the descendants of freed slaves who returned to Sierra Leone beginning in the late 1700s from Great Britain and North America and from slave ships captured on the high seas. Many thousands of Sierra Leoneans reside in the United States.

Sierra Leone's brutal 1991-2002 civil war destroyed infrastructure and truncated political, social, and economic development. The country has made substantial progress in transitioning from a post-conflict nation to a developing democracy that has made notable economic gains. It also is emerging as one of the most stable countries in a volatile region. Most notably, it now contributes significantly to United Nations peacekeeping operations, including the UN Mission to Darfur (UNAMID). It will deploy a U.S.-trained battalion to the AU Peace Support Mission to Somalia (AMISOM) early in 2013. The government also has passed one of Africa’s toughest anti-corruption laws, made high-profile arrests, and secured convictions in a majority of its prosecutions. Despite this, Sierra Leone continues to grapple with entrenched corruption, poor health conditions, weak governmental institutions, high unemployment, slow economic growth, abject poverty, and inadequate social services. In the November 17, 2012 presidential and parliamentary elections wherein over 87 percent of the electorate participated, the ruling All People’s Congress (APC) party and incumbent President Koroma were re-elected with over 58 percent of the vote in a generally peaceful process that marked the third consecutive successful election since the end of the war.

Sierra Leone relies on significant amounts of foreign assistance, principally from multilateral donors; the United States is among the largest bilateral donors. The United States is the largest single donor to the Special Court for Sierra Leone, which has pursued cases against those most responsible for violations of humanitarian law during the country's civil war.