Indio (Spanish for "Indian") is a city in Riverside County, California, United States, in the Coachella Valley of Southern California's Colorado Desert region. Indio is approximately 125 miles (201 km) east of Los Angeles, 23 miles (37 km) east of Palm Springs, and 98 miles (158 km) west of Blythe, California.

The population was 89,137 in the 2020 United States census, up from 76,036 at the 2010 census, an increase of 17%. Indio is the most populous city in the Coachella Valley, and was formerly referred to as the "Hub of the Valley," a Chamber of Commerce slogan used in the mid-twentieth century. Indio is now nicknamed the "City of Festivals," a reference to the numerous cultural events held in the city, most notably the Coachella Valley Music and Arts Festival and Stagecoach Festival.

Indio is the principal city of an urban area defined by the United States Census Bureau that is located in the Coachella Valley: the Indio–Palm Desert–Palm Springs CA urban area had a population of 361,075 as of the 2020 census, making it the 114th-most populous urban area in the United States.

Indio is within the ancestral lands of the Desert Cahuilla Indians whose headquarters are in nearby Thermal, California.

Railroad line construction east out of Los Angeles began in 1873. Trains were operated to Colton on July 16, 1875, and to Indio (then known as Indian Wells) on May 29, 1876. Moving on eastward from Indio, the railroad reached the west bank of the Colorado River opposite Yuma on May 23, 1877. Back then, Yuma was a village known as Arizona City prior to 1873. There was a delay in getting military authority to lay tracks across the Yuma Indian reservation, and it was September that year before the bridge was completed so trains could operate into Yuma. The Southern Pacific Railroad was to have joined those of the Texas & Pacific, one of several railroads then holding, or seeking, federal authority to build lines from various sections of the country west to the Pacific Coast. But the rail-head of the T & P was at a standstill far off in Texas, so Southern Pacific continued building eastward.

The City of Indio came about because of the need for a halfway point for the Southern Pacific Railroad between Yuma, Arizona and Los Angeles, since the engines needed to be refilled with water. Since other areas had the name Indian Wells, Indio (after a Spanish variation of the word "Indian") was chosen instead. After the railroad's arrival in 1876, Indio began to grow. The first permanent building was the craftsman-style Southern Pacific Depot station and hotel. Southern Pacific tried to make life as comfortable as it could for their workers to keep them from leaving such a difficult area to live in at the time. The depot was at the center of all social life in the desert with a fancy dining room and hosting dances on Friday nights.

While Indio started as a railroad town, it soon became an agricultural center. Onions, cotton, grapes, citrus and dates thrived in the arid climate due to the ingenuity of farmers finding various means of attaining water, first through artesian wells and later through the valley's branch of the All-American Canal. However, water also was a major problem for Indio and the city was flooded several times until the storm water canals were created throughout the Coachella Valley.

Businessmen and women found this last frontier land of the continental United States as an ideal place to start fresh. Dr. Harry Smiley and his wife Nell were early residents and stayed in Indio after their car broke down on the way to Los Angeles and became people of influence and helped shape the area. A. G. Tingman was an early store owner and first Postmaster of Indio, but also well known for taking advantage of miners as they headed to the mountains, selling at rather high prices. Later Dr. June Robertson McCarroll became a leading philanthropist and successful doctor in Indio. She was responsible along with the Indio Woman's Club for pressuring California into adopting the placing of white lines down the streets after she was nearly hit one too many times by passing vehicles. Even though these early founders of the city are considered pioneers, they still partook in the lifestyles of their friends living in such areas as Los Angeles.