The Rio Grande valley is a complex economic and perceptual region. What Texans call "the Valley" centers on Starr, Cameron, Hidalgo, and Willacy counties in the lower Rio Grande region and extends from the mouth of the Rio Grande up the river for a distance of some 100 miles. The lower Rio Grande contains good agricultural land, the region being a true delta and the soils alluvial, varying from sandy and silty loam through loam to clay. The area of about 4,316 square miles witnessed a tremendous development in a period of about thirty years. This spectacular development is attributable to two factors: the introduction of irrigation on a large scale in 1898 and the building of the railroad in 1904. Before that time the Valley was little more than quasi-desert rangeland. When the Spanish first occupied the area around 1750, they settled on the right bank of the river and divided the area north of the river into great cattle-ranch grants. The first American settlement in the area was Brownsville, which was founded as a result of the invasion of Zachary Taylor and the United States Army in the Mexican War (1846). The town, which sprang up around Fort Brown, remained practically the only settlement of size or distinction in the Valley for over half a century. The coming of the railroad and irrigation made the Valley into a major agricultural center. In Hidalgo County, land that had been selling for twenty-five cents an acre in 1903, the year before the St. Louis, Brownsville and Mexico Railway arrived, was selling for fifty dollars an acre in 1906 and for as much as $300 an acre by 1910. A large-scale migration of midwestern farmers in the teens and twenties, matched by a growing surge of Mexican immigration during the same period, led to dramatic population growth in Valley counties. The population of Cameron County grew from just over 16,000 in 1900 to 77,540 in 1930; that of Hidalgo County climbed from 6,534 in 1900 to 38,110 in 1920 and just over 77,000 in 1930. By 1930 the population of the four lower Rio Grande valley counties exceeded 176,000.
The lower Rio Grande valley became a curious urban and rural combination by the 1940s. Intensified agricultural development resulting from irrigation dotted U.S. Highway 83, sometimes called the "Main Street," with communities made up of homes of farm owners and workers and the various stores, processing plants, industries, and marketing agencies that served them. Farms varied in use and character from ranchland to fine citrus land. The Valley became a truck garden center for tomatoes, cabbage, carrots, potatoes, beets, corn, green beans, onions, and minor crops. Cotton and sorghum became important staples early on, but the most important crop in the region is citrus fruit. Introduced commercially in the region in 1904, citrus fruit culture has survived severe freezes in 1949, 1951, 1961, 1983 and 1989. The Valley also began to develop as a resort center in the 1940s. The year-round mild climate brought an increasing number of vacationers from the North during the winter months. McAllen, Brownsville, and other Valley communities have become winter homes for many northerners; in 1988 Hidalgo County hosted 80,000 of these "snowbirds." Fishing-freshwater, saltwater, and deep-sea-is a great attraction. Access to Mexico also promoted tourism as an important part of the Valley economy. Reynosa and Matamoros, on the Mexican side across the river from McAllen and Brownsville respectively, cater to the tourist trade, and Monterrey, Nuevo León, is only 180 miles away. The combined population of the four lower Rio Grande valley counties grew to 320,484 by 1950, then remained relatively stable through the 1950s and 1960s. The 1970s and 1980s witnessed dramatic growth in the Valley, as the population rose to 537,811 in 1980 and more than 700,000 in 1990. But in the 1980s and 1990s Hidalgo and Starr counties consistently ranked among the poorest counties in the country, partly because of a large influx of both legal and illegal immigrants from Mexico and Central America, many of whom settled in crowded and unsanitary colonias. For most of the twentieth century the region has been overwhelmingly Hispanic in population. According to the 1990 census figures, which under-reported the undocumented immigrants in the region, just under 82 percent of Cameron County, over 85 percent of Hidalgo County, over 97 percent of Starr County, and over 84 percent of Willacy County were Hispanic.
In common with other areas along the United States-Mexico border, the Valley has benefited economically from the development of maquiladoras. These industrial plants were first initiated by the Mexican government in the 1960s to encourage economic development on the border, and have become tremendously attractive to a variety of corporations as low-wage assembly and manufacturing centers. But while the maquiladoras have produced substantial industrial growth in the region, they have also had an adverse environmental impact. The region has also benefited from relaxed trade restrictions between Mexico and the United States and has become a warehouse and transportation center. In the 1990s the North American Free Trade Agreement was expected to expand employment opportunities further in the region. Agribusiness remained the mainstay of the regional economy in the 1990s. Cotton, grain sorghums, and sugarcane were leading crops in the Valley, and the region continued to be the center of citrus production and the most important area of vegetable production in the state. In 1995 Hidalgo County led the state in acres of vegetables harvested, followed by Starr and Cameron counties. Cameron, Hidalgo, and Willacy counties were the center of citrus production. Texas grapefruit, including the well-known ruby red, and navel and Valencia oranges were the most important citrus products.