Nimba County is in northeastern Liberia and shares borders with the Republic of Côte d'Ivoire in the East and the Republic of Guinea in the Northwest. Nimba is also bordered by Bong and Grand Bassacounties to the west, Rivercess County to the southwest, and Grand Gedeh County to the southeast. The northern and northeastern parts of Nimba border the nation of Republic of Guinea, while the northeast lies along the border of Côte d'Ivoire.

Named after Neinbaa Tohn Mountain, which demarcates part of the Guinea-Côte d'Ivoire border, It’s capital city is Sanniquellie and its most populous city is Ganta. With the county's area measuring 4,460 sq. miles, Nimba is the largest of Liberia's 15 counties. The county has six statutory districts and is the second most-populous county.

During the late 1950s, iron ore was found in "the Iron Mountain" Mount Nimba. In a joint venture among the Liberian Government, US Bethlehem Steel, and the Swedish mining company Gränges, a huge project was set up: LAMCO (Liberian American Company). The project contributed to economic and social development in Liberia for 30 years. It built the necessary infrastructure and operated mining, transporting ore by rail to the port of Buchanan, from where it was exported to other markets.