Liberia is divided into fifteen counties, which, in turn, are subdivided into a total of 90 districts and further subdivided into clans. The oldest counties are Grand Bassa and Montserrado, both founded in 1839 prior to Liberian independence. Gbarpolu is the newest county, created in 2001. Nimba is the largest of the counties in size at 11,551 km2 (4,460 sq mi), while Montserrado is the smallest at 1,909 km2 (737 sq mi). Montserrado is also the most populous county with 1,144,806 residents as of the 2008 census.

How many counties is liberia divided into?