The town is located in a valley nestled between Puerto Rico's Cordillera Central mountain range and the Sierra de Cayey at roughly the midpoint of routes PR-1 and PR-52.

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 Cayey was 14,442.

[4] An education base began in the early to mid-1950s when the Interamerican University opened a branch in Cayey providing teacher training through a night class scheme.

Hurricane Maria on September 20, 2017, triggered numerous landslides in Cayey with significant amount of rain and wind.

[7] Henry Barracks Military Reservation was a lifeline for the residents of Cayey from 1901 to 1966, when it was declared excess land and passed to the General Services Administration for decommission.

The Spanish Reservation containing an area of approximately 6.1 hectares (15 acres) , known as Hospital Hill was set apart by Executive Order of June 30, 1903, under an Act of Congress approved on July 7, 1902.

[10] The main army post was located in the northern part of the reservation, initially housing the Puerto Rico Volunteer Infantry Regiment.

The U.S. Department of the Navy submitted a proposal to raise three 190 metres (620 ft) tall masts as part of a global radio communication linkage.

[13] The Navy left Cayey and moved its station to Isla Grande and Stop 7 1⁄2 in Puerto de Tierra.

A full complement of maintenance personnel composed of professional, technical, and daily laborers were maintained in the Reservation.

The growth of three major housing developments is evidence of the economic impact of the Reservation (Reparto Montellano, El Polvorin, Urbanización Aponte)[18] While the all-Puerto Rican 65th Infantry regiment would never return to its home base, several other initiatives were undertaken, which had a direct impact on the economic development of the town and the region, one such initiatives was the commissioning of the Caribbean Signal Agency in 1959.

Over the coming years several tenants occupied the lands comprised by the Henry Barracks Military Reservation, among them: Cayey is located in a valley surrounded by the Sierra de Cayey, a branching mountain range of the Cordillera Central where the Carite Forest Reserve is located, and the main ranges of the Cordillera Central to the west.

Of the 742 places that were on the list in 2014, the following barrios, communities, sectors, or neighborhoods were in Cayey: Parcelas Nuevas in Beatriz, Cantera, Sector Jalda Abajo, Cedro, El Coquí, Jájome Bajo, La Placita, Saint Thomas, San Cristóbal, and La Vega.

During the 1920s and 1930s farmers increasingly lost their land to absentee landowners, mostly American companies, that turned to the cultivation of sugarcane and, to a lesser extent, tobacco for export.

In the 1950s and 1960s some manufacturing concerns established plants in Cayey taking advantage of tax incentives offered by Operation Bootstrap, Puerto Rico's industrialization program.

By 1950 the men that worked agriculture became excess population and began migrating to the United States or join the military.

The Cayey page lists the "gastronomic route" in Guavate barrio, Casa del Cuento y la Historia Cayeyana Ramón "Moncho" Gomez, Bosque de Pinos, and agrotourism at Siempre Verde, as places of interest.

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

[44] Other festivals and events celebrated in Cayey include: All municipalities in Puerto Rico are administered by a mayor, elected every four years.

[55] The coat of arms has a three tip mountain, a red bull, and a waving blue stripe representing the abundant water in the zone and also in reverence to the primitive matron of the town of Cayey.

The shield is topped with the silver lamb symbol of San Juan of Puerto Rico, and a red book.

The municipality has good paved roads and is easily accessible from San Juan, being only 25 miles (40 kilometers) away, as well as from Ponce, being only 38 mi (61 km) away.