Cayo is a district located in the west part of Belize, and it contains the capital, Belmopan.

Other important towns and cities in the district include Benque Viejo del Carmen, twin towns of San Ignacio and Santa Elena (District's Capital), Seven Miles (El Progreso), San Antonio, Valley of Peace, St. Margaret, Roaring Creek, Armenia, San Jose Succotz, Arenal, Buena Vista, Bullet Tree Falls, Calla Creek, Esperanza, Cristo Rey, Georgeville, Unitedville, Blackman Eddy, Ontario, Camalote, Los Tambos, More Tomorrow and Spanish Lookout.

In 1960, the boundaries of the Cayo District were defined as follows:[3] Commencing at Big Falls, Belize River; thence upward along the course of the Belize River to Labouring Creek, Yalbac Creek and Tu-Tu Creek to the Western Frontier Line; thence following the Frontier Line southward to the crossing of the main divide or watershed of the Maya Mountains; thence in a north-easterly direction along the main divide of the Maya Mountains which forms the watershed between Machiquila River, Belize River and Sibun River systems on the west and north, and Moho River, Rio Grande, Monkey River, Sittee River and North Stann Creek systems on the east and south to the top of the peak known as Arthur's Seat west of Middlesex; thence by a direct line in a north-north-easterly direction to the highest point on the Humming Bird Highway in the Humming Bird Gap; thence by the southern side of the Humming Bird Highway in a westerly direction to a point 70 chains east of St. Margaret's Creek bridge measured along the Highway; thence in a straight line in a northerly direction to the source of the westernmost tributary of Indian Creek; thence downward along the courses of Indian Creek and Sibun River to the mouth of Nancy Porter Creek; thence in a straight line to the point of commencement.As of 2020, these are still the boundaries used for the District.

Politically, Cayo is divided into six constituencies, described in detail here: Cayo District contains several pre-Columbian mayan ruins and sites, among these are Caracol, Xunantunich, Cahal Pech,[5] Baking Pot, Lower Dover and El Pilar.

A large majority of the district's population lives north of the 17th parallel.