Southwest Idaho’s Treasure Valley has added roughly 150,000 residents over the past six years, according to new population estimates accepted by the Community Planning Association of Southwest Idaho (COMPASS) at its April 27 board meeting. The figures confirm that Ada and Canyon counties — long a small-city corridor — have solidified their status as one of the fastest-growing metropolitan areas in the American West, with profound implications for infrastructure, housing, and public services across Ada County and beyond.
By the Numbers: Boise, Meridian, and Kuna Lead Ada County Growth
The combined population of Ada and Canyon counties now stands at 876,760, up from 726,072 recorded in the 2020 Census. When Boise and Elmore counties are added to the calculation, the four-county regional total climbs to 915,940 — representing more than 20% growth in just six years. The two-county area has more than tripled in size since 1990, when Ada and Canyon counties together held approximately 295,000 residents.
Within Ada County, the growth is hard to miss. Boise, the state capital, reached a population of 256,450, maintaining its rank as Idaho’s largest city. Meridian added 4,730 residents in the past year alone to hit 152,070, cementing its position as Idaho’s second-largest city. Kuna, located on Ada County’s southwestern edge, posted a striking 14% single-year increase, growing by 4,810 people to reach 38,560. That kind of growth rate, sustained year after year, places enormous pressure on local roads, schools, and utilities.
For Ada County families and taxpayers, the pace of expansion raises practical questions about how local governments will fund the infrastructure needed to keep up. Boise State University’s planned student union renovation and $8.5 million investment reflects the broader theme of institutions scrambling to accommodate a rapidly expanding population base.
Smaller Communities See Staggering Percentage Gains
While the large cities generate the biggest raw numbers, the most dramatic transformation is unfolding in the region’s smaller communities. Star, a small city in Ada County that counted just 11,107 residents in the 2020 Census, has exploded to 24,950 — a 131% increase in six years, the highest percentage gain of any city in the COMPASS coverage area. Like Kuna, Star also grew 14% in a single year.
Middleton, located in neighboring Canyon County, has grown from 9,425 to 15,110 since 2020, a jump of more than 60%. These outlying communities are absorbing growth that larger cities can no longer easily accommodate, driven largely by housing affordability pressures and a desire for more land and lower density.
Austin Miller, COMPASS planning team lead, noted the contrast between large and small city growth rates. “The percentage of growth in some of our smaller communities is staggering,” Miller said. “Cities like Kuna and Star each grew by 14% in just one year, as compared to larger cities such as Meridian and Nampa that each grew by 3% in the same period.”
Miller added that the distinctions underscore the value of examining growth data across multiple dimensions — raw numbers, percentage change, year-over-year shifts, and comparisons to census baselines — rather than relying on any single metric.
Impact on Ada County Residents and Taxpayers
For Ada County residents, population growth is both an economic asset and a logistical challenge. More residents mean a broader tax base and greater consumer demand — good news for small businesses, local restaurants adapting to a changing market, and employers looking to hire. But growth also drives up housing costs, strains transportation networks, and stretches school capacity.
Interstate 84, the main artery through the Treasure Valley, has seen worsening congestion as the regional population climbs. Traffic delays that were once associated with peak commute hours have become routine throughout the day. Planning agencies and local governments face mounting pressure to deliver road improvements, water and sewer infrastructure, and public services at a pace that matches residential expansion — all while keeping tax burdens manageable for existing homeowners and businesses.
Not all communities are under pressure. The small Canyon County towns of Greenleaf and Notus showed essentially flat population figures between 2025 and 2026, and unincorporated areas in both counties saw little measurable change. Nampa, Canyon County’s largest city, grew modestly to 126,810 after experiencing faster expansion in prior years.
What Comes Next
COMPASS compiles its annual estimates using building permits, household size data, vacancy rates, and annexation records. The estimates serve as a planning foundation for transportation projects, utility expansions, and land-use decisions across the region. Full population figures and historical comparisons are available at compassidaho.org.
Local governments in Ada County, including Boise, Meridian, Kuna, and Star, will use the updated figures as they prepare budgets, review infrastructure needs, and update comprehensive plans. Residents interested in how population growth affects local planning decisions can attend public meetings hosted by COMPASS or their individual city councils, where growth projections regularly shape discussions about roads, housing, and public services.