Ada County, located in southwestern Idaho, is the most populous county in the state and home to its capital, Boise. Formed in 1864 during the Idaho Territory period, the county has a rich history rooted in the region’s mining, agricultural, and transportation industries. Originally part of the Oregon Trail route, Ada County evolved from a small mining hub into a bustling center of government, commerce, and culture. Today, Ada County serves as Idaho’s economic and political heart, reflecting its complex past while embracing modern growth and development.
Origins of Ada County
Ada County’s origins are closely tied to the broader history of westward expansion in the United States. The area now known as Ada County was originally inhabited by Native American tribes, including the Shoshone and Bannock peoples, who used the Boise River Valley for fishing, hunting, and gathering. In the early 19th century, fur trappers and explorers, such as the members of the Lewis and Clark Expedition, traveled through the region, marking the beginning of European-American exploration in the area.
The Oregon Trail and Early Settlement
One of the most significant influences on the development of Ada County was the Oregon Trail. From the 1830s through the 1860s, thousands of pioneers crossed the vast plains and deserts to reach the fertile lands of the Pacific Northwest, with many passing through the Boise River Valley. Fort Boise, established by the Hudson’s Bay Company in 1834, provided a critical waypoint for emigrants heading westward.
As gold was discovered in Idaho during the 1860s, the population of the region exploded. The town of Boise was founded in 1863, and Ada County was officially created the following year, named after Ada Riggs, the daughter of one of Boise’s founders. The county quickly became an important center for trade and transportation, especially with the establishment of stagecoach routes and, later, the arrival of the railroad in the late 19th century.
Growth During the 19th Century
The late 19th century saw steady growth in Ada County, as Boise became the territorial capital of Idaho in 1864 and, eventually, the state capital when Idaho gained statehood in 1890. The county’s economy was initially based on agriculture and mining, but it expanded rapidly with the construction of irrigation systems that transformed the arid landscape into fertile farmland. Settlers grew crops such as wheat, potatoes, and sugar beets, establishing Ada County as an agricultural hub in Idaho.
The Boise River, running through the heart of the county, played a crucial role in the area’s agricultural success, providing water for irrigation as well as transportation routes for goods and services.
Key Historical Events in Ada County
Over the course of its history, Ada County has experienced several key events that have shaped its development into Idaho’s most populous and economically significant region.
The Establishment of Fort Boise (1834 and 1863)
The first Fort Boise, established in 1834 by the Hudson’s Bay Company, was located near the confluence of the Boise River and the Snake River. It served as an important trading post for fur trappers and a rest stop for pioneers along the Oregon Trail. However, this fort was eventually abandoned due to frequent flooding and conflicts with Native American tribes.
A second Fort Boise was established by the U.S. Army in 1863 near present-day Boise to protect settlers and maintain order during the gold rush. The establishment of this military fort coincided with the founding of Boise, which quickly grew into a major settlement and ultimately the capital of Idaho Territory.
Idaho Statehood and Boise’s Rise as the Capital (1890)
When Idaho became a state in 1890, Boise solidified its position as the state’s political and economic center. The city’s strategic location on the Boise River and its growing infrastructure, including the arrival of the railroad in 1887, helped it outpace other Idaho cities in terms of growth and importance.
Construction of the New York Canal and Agricultural Boom (Early 20th Century)
The early 20th century marked a significant period of growth for Ada County’s agricultural industry. One of the most transformative projects was the construction of the New York Canal, completed in 1909 as part of the larger Boise Project. This irrigation canal diverted water from the Boise River, making thousands of acres of land in Ada County suitable for farming.
The availability of water spurred an agricultural boom, with the region becoming a major producer of crops such as sugar beets, potatoes, onions, and fruit. The canal system also allowed the population of Ada County to expand, as more settlers moved into the area to take advantage of the fertile land.
The Growth of Boise and World War II Era (1940s)
During World War II, Ada County experienced a population surge as Boise’s economy grew due to military and defense contracts. The nearby Gowen Field, originally a municipal airport, was transformed into a training base for the U.S. Army Air Forces. This brought thousands of soldiers and workers to the area, boosting the local economy and leading to post-war development.
Following the war, Boise and Ada County continued to grow, as infrastructure improvements and the expansion of the interstate highway system made the region a key transportation and logistics hub.
Historical Sites in Ada County
Ada County boasts several historical landmarks that reflect its rich history and cultural heritage. These sites provide insight into the county’s past and offer visitors the chance to explore Idaho’s frontier and early statehood eras.
Old Idaho Penitentiary
Overview
The Old Idaho Penitentiary, located in Boise, operated as a prison from 1872 to 1973 and housed some of Idaho’s most notorious criminals. Today, the site is preserved as a museum, offering visitors a glimpse into the life of prisoners during the late 19th and early 20th centuries. The prison complex includes several historic buildings, such as the cell blocks, the gallows, and the solitary confinement area known as “Siberia.”
Location
2445 Old Penitentiary Road, Boise, Idaho.
Ticket Price
Admission is $8 for adults, $6 for seniors (60+), and $5 for children (ages 6-12). Children under 6 are free.
Parking Information
Free parking is available on-site.
Idaho State Capitol Building
Overview
The Idaho State Capitol, located in downtown Boise, is one of the most iconic landmarks in the state. Completed in 1920, the building is constructed from locally sourced sandstone and marble. Visitors can tour the Capitol to learn about Idaho’s legislative process and admire the building’s grand architecture, including its majestic dome and interior rotunda.
Location
700 W Jefferson Street, Boise, Idaho.
Ticket Price
Admission is free, and guided tours are available upon request.
Parking Information
Street parking is available around the Capitol, with several paid parking lots located nearby.
Julia Davis Park and Zoo Boise
Overview
Julia Davis Park, established in 1907, is one of Boise’s oldest and most beloved parks. Donated by Thomas Davis in honor of his wife Julia, the park is home to several cultural attractions, including Zoo Boise, the Boise Art Museum, and the Idaho Historical Museum. The park is a central gathering place for both locals and visitors and offers a variety of recreational activities.
Location
700 S Capitol Boulevard, Boise, Idaho.
Ticket Price
Admission to Julia Davis Park is free. Zoo Boise has a separate admission fee: $11 for adults, $8 for seniors (62+), and $7 for children (ages 3-11). Children under 2 are free.
Parking Information
Free and paid parking is available throughout the park, with several lots located near major attractions.
Basque Block
Overview
Boise is home to one of the largest Basque communities in the United States, and the Basque Block celebrates this unique cultural heritage. The area features the Basque Museum & Cultural Center, which highlights the history of Basque immigrants in Idaho, as well as traditional Basque restaurants and shops. Visitors can learn about Basque traditions, language, and customs, as well as experience cultural events like the annual Basque Festival.
Location
601 W Grove Street, Boise, Idaho.
Ticket Price
Admission to the Basque Museum & Cultural Center is $5 for adults, $3 for seniors (65+), and $3 for students. Children under 5 are free.
Parking Information
Paid street parking is available around the Basque Block, and there are public parking garages nearby.
County Facts About Ada
Geography and Climate
Ada County is situated in the southwestern part of Idaho and covers 1,060 square miles. The county is part of the Snake River Plain, a geologically diverse area characterized by its flat plains, rolling hills, and nearby mountain ranges. The Boise River runs through the center of the county, providing water for agriculture and recreational activities.
The county experiences a semi-arid climate, with hot, dry summers and cold winters. Average summer temperatures range from the mid-80s to low 90s °F, while winter temperatures can dip into the 20s. Snowfall is common in the winter months, especially in the higher elevations surrounding the Boise foothills.
Key Facts at a Glance
- Year Founded: 1864
- County Seat: Boise
- Population: Approximately 511,000 (as of the 2020 census)
- Population Density: About 482 people per square mile
- Largest Cities: Boise, Meridian, Eagle, Kuna, Star
- Major Highways: Interstate 84, U.S. Route 20, U.S. Route 26, U.S. Route 95
- Adjacent Counties:
- Canyon County (west)
- Elmore County (east)
- Gem County (northwest)
- Owyhee County (south)