Calexico was one of five townsites laid out by the Imperial Land Company in October 1900 (the others being Imperial, Brawley, Heber, and Silsbee) as part of the colonization of Imperial Valley. Though Imperial was developed first, Calexico became the headquarters for the California Development Company - the company responsible for bringing irrigation to the desert. Due to an initial lack of water in Calexico, growth was slow, but after water reached the townsite in June 1901 it took off. Sorghum, wheat, and barley and test crops of cantaloupe and cotton were planted and met with success; by the end of the year over 8000 acres had been started and another 70,000 had been filed.

Calexico continued to grow for the next few years as a trading center. An official border crossing into Mexico was established in 1902. On June 29, 1904 the Imperial & Gulf Railroad reached town, linking Calexico to the Southern Pacific at Imperial Junction, a distance of forty miles, with rails continuing south into Mexico as the Southern Pacific's Inter-California Railway. That year, Calexico's Mexican neighbor - the similarly named Mexicali - began to develop and the Calexico Chronicle had its first publication; that paper still exists today.

In 1905, it was almost all washed away. An unusually wet winter, combined with silt buildup in the Imperial Canal, led to the Colorado River overflowing its banks and flooding the Imperial Valley. The largest flood sent the entire flow of the mighty river down into the valley via two dry ravines: the Alamo River and New River (as the Imperial Valley lays below sea level, there was no other outflow; ultimately this flooding created the Salton Sea). As Calexico is situation directly adjacent to the New River's channel, it was quickly apparent that something needed to be done to protect the town. Under the direction of Engineer C.N. Perry, the residents of Calexico built a six foot levee on the river side of town using every resource available. For two days, the town worked tirelessly to protect themselves until the floodwaters receded to a safe level. Calexico was saved, though nearly 20,000 acres were either flooded or destroyed. Damages in Calexico amounted to roughly $15,000; in nearby Mexicali they amounted to nearly $75,000. The town rebuilt, though the flow of the Colorado wasn't controlled and routed back to the correct channel until February 10, 1907.

After the floods subsided, Calexico continued to grow. It was incorporated as a city on April 16, 1908 and through the remainder of the decade received a number of improvements. By 1910, Calexico had 800 residents and stores, churches, the brick Calexico Hotel, and a school and high school. A sewer system was installed in 1911. Unfortunately, distaster once again struck on June 22, 1915. Back to back earthquakes leveled much of the town, causing $300,000 in damage; there were no casualties in Calexico, though again Mexicali wasn't so fortunate. Again, Calexico rebuilt, gaining new schools and even a Carnegie library and City Hall. By 1920, the population exceeded 6000.

Over the past century, though shaken by a number of large earthquakes (most notably the 7.2 magnitude Baja California earthquake on April 4, 2010), Calexico has always rebuilt itself, growing to become the second largest city in Imperial Valley, with a population of nearly 40,000. It's border crossing, which was supplemented with a second crossing to the east in 1996, is the United States' fifth busiest crossing into Mexico. As such, most of Calexico's economy is now based on travel and tourism between the two countries. A number of historic buildings still stand at the core of the city, though many of their appearances have been altered due to earthquake damage over the years.

See Also
Jasper-Alamitos Union School