Puerta de Tierra is a subbarrio (subdistrict) occupying the eastern portion of the Islet of San Juan and the barrio of San Juan Antiguo in the municipality of San Juan, Puerto Rico. The name Puerta de Tierra (Spanish for land gate) derives from the former eastern gated entrance to the walled city of San Juan where Plaza Colón (formerly Santiago Square, named after the Puerta de Santiago) is today. With a population of 2,924 as of 2010, this is the most populated area of San Juan Antiguo. On October 15, 2019, it was added to the National Register of Historic Places.

Before the arrival of the Europeans to Puerto Rico, Puerta de Tierra (along with Old San Juan) formed part of a smaller islet which was populated by the Taíno. Remains of a small indigenous fishing village have been found where the Puerto Rico National Guard Museum stands today, however most archaeological sites in the area have been destroyed and lost during the construction of the Muñoz Rivera Avenue and surrounding buildings.

The Spanish began the colonization of Puerto Rico in 1508 when Juan Ponce de León founded Caparra, the first permanent settlement in the island, located in the southern part of the Bay of San Juan (today part of Guaynabo). This Spanish village was abandoned in 1519 when the Spanish founded the settlement of Puerto Rico de San Juan Bautista (modern-day Old San Juan) across the bay. The area where Puerta de Tierra is located became critical for the settlement and the defense of the Islet of San Juan as it represented the closest part of the islet to the main island of Puerto Rico. This area, later referred to as El Boquerón, was separated from the main island by the San Antonio strait (today known as the San Antonio Channel). The first bridge across the San Antonio Channel was built by enslaved Taínos between 1520 and 1521 as entrusted by the Order of Saint Jerome (or Hieronymites).

One of the first witch-hunts in the New World occurred in Puerta de Tierra in 1594 when bishop and inquisitor Don Nicolás Ramos accused a group of people of African descent of celebrating pagan rituals just outside of the settlement of San Juan. The accused were tortured and forced to reject their beliefs, although three women who did not comply were burned at the stake by orders of the Holy Inquisition.

Construction of the fortified wall system of San Juan began in 1634. Although the area outside the city walls occupying the east side of Old San Juan was almost uninhabited prior to the 19th century, this area represents the first urban expansion of San Juan during the colonial period. Some of the settlers of the area around this time were freed families originating from the British, Dutch and Danish colonies in the Caribbean. While most residences were wooden huts and bohíos, this represents the first eastward demographic expansion of the colonial city of San Juan. Most of the huts were located along the eastern walls and the Puerta de Santiago (Santiago Gate). Due to the fact that this was the main entrance by land to the fortified city, the gate was referred to as Puerta de Tierra.

The area was further settled after the eastward expansion of the batteries of Fort San Cristóbal in 1771 and the construction of the Camino Real (today the Ponce de León Avenue) later in 1810. The area was attacked by the British during the 1797 Battle of San Juan under the command of Sir Ralph Abercromby and Sir Henry Harvey, during the Coalition Anglo-Spanish War. The British invasion was thwarted by the local Spanish militia and regiments of Afro-Puerto Ricans after an unsuccessful siege of San Juan. This event led to the re-fortification of El Boquerón in the eastern end of Puerta de Tierra. Remnants of these military installations can still be seen today in the Luis Muñoz Rivera Park. By 1838, Puerta de Tierra had a population of 168 residents, mainly of African descent.

Although the military installations in San Juan were modernized in 1865, the eastern portion of the walls were no longer deemed necessary due to the eastward expansion of the city and were consequently partially demolished. The 1867 Virgin Islands earthquake destroyed the remaining eastern military installations in the area, and a new road and railway station were built with the name of Paseo Virgen de Nuestra de Señora de Covadonga and the Covadonga Terminal, respectively. The Paseo Covadonga exists today under the name of Covadonga Avenue. The San Juan streetcar system was developed along the Camino Real in 1880, during a time when the southern coast of Puerta de Tierra began to be industrially developed as piers and docks were installed along the San Antonio Channel. During this time, Puerta de Tierra became the most populated area in the Islet of San Juan, which is reflected through the construction of a new parish church (Church of San Agustín), bullfight arenas, schools and new streets. Although the area was quickly developing, most of the residential structures were unplanned, something that also happened along the northern walls of the city in La Perla.

The United States took control of Puerto Rico from Spain in the aftermath of the Spanish–American War under the terms of the Treaty of Paris of 1898. In 1899, the United States conducted its first census of Puerto Rico, finding that the population of Puerta de Tierra was 5,453. Puerta de Tierra was badly damaged during the path of the San Ciriaco hurricane (also known as the 1899 Puerto Rico Hurricane).