Founded by the Spanish in 1579, Coamo was the third city established in Puerto Rico. It dominated the south of the island until the mid-1880s, when political power shifted to Ponce. The town, however, remained an important outpost; several decisive battles were fought here during the Spanish–American War in 1898.
The thermal springs outside Coamo are believed by some to be the Fountain of Youth for which Ponce de León was searching. In the mid-1800s, a fashionable resort was built nearby, and people have been coming to soak in the waters ever since. Coamo is also famous for the San Blás Half-Marathon, which brings competitors and spectators from around the world. The race, held in early February, covers 18 km (13 miles) of the city's hilly streets.