Pharr is on the Missouri Pacific line and old U.S. Highway 83 (now Interstate Highway 2), just to the east of McAllen in south central Hidalgo County. Its site is within a Spanish land grant made in 1767 to Juan José Hinojosa. The Hinojosa family and heirs sold off portions of their land to various groups in the late nineteenth century and occupied the area as late as 1882. In 1909 John Connally Kelley, Sr., and Henry N. Pharr, a Louisiana sugarcane grower, became co-owners of 16,000 acres, with two miles of frontage on the river. Pharr founded the Louisiana and Rio Grande Canal Company and constructed an irrigation system to establish a sugar plantation. Kelley formed the Pharr Townsite Company, which platted the town that he named Pharr in honor of his partner. By 1911 the community was a stop on the St. Louis, Brownsville and Mexico Railway, and 4,000 acres had been sold for settlement. A hotel, a bank, and various businesses were also in operation. Pharr's plantation venture failed with the collapse of the Rio Grande valley sugarcane industry. Kelley then took over the irrigation system and continued to supply water to area vegetable and cotton farms. In 1915 the town's population was estimated at 600, and by that year schools had opened, with Mexican students attending classes at the six-grade East Juárez school. When the site for the school was moved, it became known as Pharr Grammar School for Mexican Children. Separate facilities for junior and senior high school students were not provided because Mexican children were not expected to get beyond grammar school.
Pharr incorporated in 1916, and W. E. Cage established the Rio Grande Clarion newspaper and the National Theatre there. In 1919 Pharr, San Juan, and Alamo established the Pharr-San Juan-Alamo Independent School District. By 1920 Pharr had an estimated population of 1,560. In 1925 Mexican students requested that they be allowed to attend high school with the other children. By 1931 Pharr had a population of 3,225 and 105 businesses; by 1940 its population was 4,784. Pharr adopted a home-rule charter and a commission government in 1949. In 1956 a move to merge the town with neighboring McAllen was put to a public vote and defeated. The population of Pharr increased from 8,690 in 1950 to 14,106 in 1960. Businesses reported there in the 1960s included manufacturers of irrigation equipment, clay products, mattresses, food harvesting and processing equipment, and concrete products. In 1970 Pharr had 212 businesses and an estimated population of 15,829.
Segregated schools continued to be the norm for the school district as late as the 1970s, on the grounds of language differences, geography, ethnic preference, and economics. That segregation was a problem became evident in 1971, when the "Pharr Police Riot" occurred. At the time the city was divided along economic and ethnic lines, with Caucasians living south of the railroad tracks and Mexican and African Americans on the north side. Grade schools were segregated by these residential patterns. On February 6, 1971, local Mexican Americans demonstrated in front of the police station and were fired on by police officers. Alfonso Loredo Flores, a bystander, was shot by a deputy sheriff. The media attention led to an investigation and a restructuring of city government. In 1980 Pharr had a population estimated at 19,483 and 327 businesses. In 1990 its population was 32,921. In 2000 the population was 46,660 with 1,238 businesses. By 2010 the population reached 70,400. The town's growth can be attributed in part to the growth of nearby McAllen, the annexation of several unincorporated "colonias" nearby, the increasing number of births among the young Hispanic population, and the movement of vacationers and retirees to the area because of its warm climate. The opening of the Pharr-Reynosa International Bridge in 1994 also helped make Pharr a major commerical port of entry.