Mértola, officially known as the Town of Mértola, is a town and municipality located in the southeastern region of Portugal's Alentejo province. It is situated near the border with Spain.
The municipality covers an area of approximately 1,292.87 square kilometres (499.18 mi2), making it the sixth-largest municipality in Portugal. As of 2021, its population was 6,206 people. It is characterized by a very low population density, ranking as the second-lowest population center in the country with approximately 5.62 persons per square kilometre (0.39 mi2).