People have lived in this area for over 5,000 years. The Tatcan Indians, a Bay Miwok tribe closely connected to the Saclans of Walnut Creek, lived in Alamo in the eighteenth century.
After Mission San José was founded in 1797, its grazing area stretched throughout the San Ramon Valley. The Mexican land grant Rancho San Ramon was deeded to Mariano Castro and his uncle Bartolo Pacheco in 1833. It covered today's Danville and Alamo. Castro owned the northern half, which included Alamo.
In 1843 much of the Alamo, Las Trampas and Tice Valley areas were granted to brothers Inocencio and Jose Romero. It was called Rancho El Sobrante de San Ramon. Because of missing title papers, the brothers lost their ranch in American courts in 1857.
Other early Alamo founders included David Glass, George Engelmeyer, Silas and Susanna Stone, Captain Wall, Joshua Bollinger, and James Foster.
The area was named Alamo, which means "poplar" or "cottonwood" in Spanish. Because of its location and fine weather, Alamo grew quickly. An early road from the redwoods near Moraga ran through Tice Valley to Alamo, since Americans preferred redwood for building materials instead of Mexican adobe brick.
The Hemme, Bollinger, Jones and Stone ranches began by grazing cattle and raising wheat and other grains. In 1891 the Hemme train station was placed near today's Hemme Avenue; later it was renamed the Alamo station.
Eventually orchards and vineyards spread across the area. Almonds, walnuts, pears, grapes and other fruit thrived in the mild climate. In 1873, Alamo pioneer Myron Hall grafted Persian cuttings to native walnut trees and helped start the prosperous walnut industry in Contra Costa County. This "mother tree" was tended for over 100 years.
The Alamo post office is the oldest continuously operated one in the valley. It was always an important community gathering place.
During World War II, an Alamo air watch tower was built by the community. Volunteers watched for Japanese war planes round the clock from 1942 to 1945. San Ramon Valley's population totaled 2,126 at that time.
The Alamo Improvement Association (AIA) began in 1953. For 50 years its purpose has been to advance and improve the welfare of properties in Alamo and to preserve the established character of Alamo as an agricultural and semi-rural residential area.
After the war, hundreds and then thousands of new people arrived. Round Hill Country Club opened in 1960 on land that had belonged to the Mott sisters and Grover Squire. In 1964, Interstate 680 was completed through San Ramon Valley, which encouraged even more growth.
Today Alamo is an enclave of green between Walnut Creek and Danville. Its population in 2010 was 14,750. It is governed by the County Board of Supervisors, with the AIA and several active county service areas advising on police, landscape and park issues.