Juncos (Spanish pronunciation: [ˈxuŋkos]) is one of the 78 municipalities of Puerto Rico and is located in the eastern central region of the island, south of Canóvanas and Carolina; southeast of Gurabo; east of San Lorenzo; and west of Las Piedras. Juncos is spread over 9 barrios and Juncos barrio-pueblo (the downtown area and administrative center of the city). It is part of the San Juan-Caguas-Guaynabo Metropolitan Statistical Area.
Juncos was founded on the request of Tomás Pizarro on August 2, 1797, having previously been a village which evolved from a small ranch, the Hatillo de los Juncos. This ranch was part of the Hato del Valenciano, which gave its name to the Río Valenciano which bisects the city before joining the Río Gurabo to the north of the settlement.
During the 17th century, large parts of the municipality were owned by the Hato Grande de los Delgado (The Delgados' Great Ranch). Another ranch, the Hato del Valenciano (Valencian's Ranch), was established and later divided into the Hatillo de los Lirios (Small Ranch of the Lilies) and the Hatillo de los Juncos (Small Ranch of the Reeds). This second one became the village of Juncos in the 18th century and was given the status of a town on August 2, 1797. Reeds, which gave the city its name, feature in the center of its flag and the bottom of its coat of arms. The Hato del Valenciano is remembered in the name of the Río Valenciano, as well as the coat of arms of Valencia featuring in Juncos' coat of arms, in addition to the city's two nicknames of La Ciudad del Valenciano (The Valencian's City) and Los Mulos del Valenciano (The Valencian's Mules).
Hurricane Maria on September 20, 2017 triggered numerous landslides in Juncos with the significant amount of rainfall.
On the flag of Juncos, on a gold field, blue waving stripes cross horizontally in the lower half.