[3] Puerto Rico was ceded by Spain in the aftermath of the Spanish–American War under the terms of the Treaty of Paris of 1898 and became a territory of the United States.

In 1899, the United States Department of War conducted a census of Puerto Rico finding that the population of Juncos was 8,429.

The upper right quarter is blue with twelve silver stars to represent the Virgin Mary, and also features a cross confirming the city as part of Christendom.

Underneath the shield lie the red-budded green reeds which gave the city its name, which features alongside its year of foundation (1797) at the very bottom.

The Fiestas Patronales Inmaculada Concepcion de Maria is a religious and cultural celebration that generally features parades, games, artisans, amusement rides, regional food, and live entertainment.

[11] Other festivals and events celebrated in Juncos include: In the fertile plains of the Río Valenciano, coffee, fruits, sugar cane and tobacco are grown.

The lower left quarter of the municipal coat of arms pay homage to tobacco cultivation and sugar cane processing.

Apparel, electronic machinery and electrical equipment, scientific instruments, pharmaceutical and biotechnology industries Amgen, a biopharmaceutical company, has developed its largest manufacturing site in Juncos.

[33] Amgen Puerto Rico received FDA approval for bulk manufacturing facilities for Nepogen (filgrastim), Neulasta (pegfilgrastim), Aranesp and Epogen.

Roberto Clemente Walker, later a double-World Series winner for the Pittsburgh Pirates, played baseball for Juncos before signing with the Santurce Crabbers in Puerto Rico's Professional League.

In the year 2006–2007 the Valencianas de Juncos won the women's basketball and volleyball superior league national championship.

The team moved to Juncos due to ownership and financial problems and currently play in the Alfredo "Papo" Alejandro Stadium.