Mazarrón is a municipality in the autonomous community and province of Murcia, southeastern Spain. The municipality has an area of 318.7 square kilometres, and a population of 31,562 inhabitants in 2019. A military fort which was built between 1930 and 1936 during the reign of Alfonso XIII of Spain and the Second Spanish Republic exists as a tourist attraction on the old road between Mazarrón and Cartagena, and although it is accessible from the Bay of Mazarrón it is not in the municipality itself.