Lajas was the last village to separate from the municipal territory of San Germán on July 1,1883. Lajas is divided into 11 neighborhoods and Lajas Pueblo, the urban and administrative center of the Municipality of Lajas. The extinct Taíno Indians are considered the first settlers of the territory. The first settlement was in the eighteenth century by Spaniards and Creoles of San Germán near a spring with smooth stones known as "lajas", hence its name. Don Teodoro Jacome Pagán is considered as its founder along with other families of Mallorcan Hebrew converts. Lajas gradually developed for the sowing of sugarcane in his valley and fishing on the coast. Later the planting of pineapples, especially the big one, will be developed by local farmers.
In 1907, Juan Cancio Ortiz founded the Institute of Agriculture, Arts and Crafts in the Palmarejos neighborhood, which later moved to the neighboring city of San Germán and became the current Inter-American University of Puerto Rico. In the middle of the 20th century, the area of La Parguera became a tourist center due to its Phosphorescent Bay, the mangrove channels and the shellfish production. In 1973, the Cardinal title of the Catholic Church was conferred on Luis Aponte Martínez, an act that arouses his current motto of "Ciudad Cardenalicia" and -also- is reflected in the municipal coat of arms. In the year 1883, the celebration of the centenary of the founding of Lajas provokes a series of works and events such as the adoption of the shield and the anthem, tributes to outstanding artists, the publication of the book 'History of Lajas, the creation of new recreational facilities and the remodeling of others.
The first Festival of Chiringas and Tigüeros de Lajas is celebrated. At the end of the 20th century, the population increases significantly to its current number, new roads and public and commercial facilities are developed, and Lajas is recognized as one of the cleanest towns in Puerto Rico, being its last distinction in 2004.