Treasure Valley population grows by 150,000 in six years

Southwest Idaho added roughly 150,000 residents in six years, according to new population estimates that underscore the region’s continued transformation from small-city corridor to major metropolitan area.

The Community Planning Association of Southwest Idaho (COMPASS) accepted its 2026 population estimates at a board meeting April 27, putting the combined population of Ada and Canyon counties at 876,760, which is up from 726,072 in the 2020 Census. When Boise and Elmore counties are included, the four-county total reaches 915,940, a figure that represents more than 20% growth since 2020.

The numbers tell different stories depending on where you look. The headline figures belong to the region’s largest cities: Meridian added 4,730 residents in the past year alone to reach 152,070, making it the second-largest city in Idaho behind Boise, which grew to 256,450. Caldwell added 5,160 people to reach 82,770, and Kuna gained 4,810 to reach 38,560, a 14% single-year jump that mirrors the pace of growth in Star, which also grew 14% in the same period.

But the longer-term picture belongs to smaller communities on the region’s edges. Star, which counted just 11,107 residents in the 2020 Census, now stands at 24,950, a 131% increase in six years; the greatest percentage gain of any city in the COMPASS coverage area. Middleton in Canyon County has grown from 9,425 in 2020 to 15,110, an increase of more than 60% in the same span.

“While our population growth is spread throughout the region, the percentage of growth in some of our smaller communities is staggering,” said Austin Miller, COMPASS planning team lead. “For example, the cities of 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. These distinctions underscore the importance of looking at the data from multiple viewpoints, such as numeric growth, percent growth, change year-over-year and change as compared to the most recent census count.”

Not every community is growing. The populations of Greenleaf and Notus in Canyon County remained essentially flat between 2025 and 2026, and unincorporated areas in both Ada and Canyon counties showed little change. Nampa, Canyon County’s largest city, grew modestly to 126,810 after years of more rapid expansion.

Taken together, the Ada and Canyon counties’ population has more than doubled since 1990, when the two-county area held roughly 295,000 residents. The trajectory shows little sign of slowing: The region has added population every year since the 2020 Census with no single jurisdiction recording a significant decline.

COMPASS calculates its annual estimates using building construction permits, household sizes, vacancy rates and annexation data. Full estimates and historical comparisons are available at compassidaho.org.

This story was written using artificial intelligence with human oversight.