Private Swap - Puerto Rico

As an unincorporated territory of the United States, Puerto Rico does not have any first order administrative divisions as defined by the U.S. Government, but there are 78 municipalities at the secondary level which function as counties. Each municipality has a mayor and a municipal legislature elected for four year terms.

The first municipality (previously called "town") of Puerto Rico, San Juan, was founded in 1521. (source)

Thank you Emy!