Idaho's Lopsided Geography: Boise Reaches 51.8% of the State Inside 100 Miles
51.8% of Idaho’s population — about 933 K of 1.80 M residents — lives within 100 miles of Boise. The other 48.2% — including Idaho Falls — sits beyond the circle.
The link opens the SimpleMapLab Map Radius Tool with the 100-mile circle already drawn around the Boise capitol. Change the radius to 50, 250, or any value to compare different framings.
Why this happened
Idaho is a "split" state by this measure: roughly half its residents live within an hour and a half of the capital, and roughly half live beyond. Boise's 100-mile reach captures Boise (~268K) and the surrounding counties, but stops well short of Idaho Falls, which sits 217 miles away. The capital-to-population-centroid distance is 64 miles — a clear signal that political and demographic weight no longer share a single point on the map.
The biggest cities inside the 100-mile radius
The top 5 most-populous places (by aggregated ZIP code population) sitting inside the 100-mile circle around Boise. Cities are listed by total population captured by ZIP centroids in the dataset.
| # | City | Population in radius |
|---|---|---|
| 1 | Boise | 267,769 |
| 2 | Nampa | 142,249 |
| 3 | Meridian | 138,302 |
| 4 | Caldwell | 76,816 |
| 5 | Kuna | 36,286 |
The largest city outside the radius
Idaho’s most-populous city outside the 100-mile circle is Idaho Falls, sitting 217 miles from Boise. The aggregated population of Idaho Falls’s ZIP codes alone — 125,162 residents — illustrates the gap between Idaho’s political seat and its population centre.
How Idaho compares
The states ranked closest to Idaho on this metric. Click any to compare the radius breakdown directly.
Draw it yourself
Open the 100-mile circle around Boise →
The Map Radius Tool lets you change the radius (try 50 mi for an urban-suburban question or 250 mi for “a day’s drive”), drag the centre to compare Boise’s reach with that of Boise, or add a second circle for a side-by-side comparison.
Methodology (brief)
We took the lat/lng of the Idaho state capitol building (43.6150°, -116.2023°) and drew a 100-mile geodesic radius. For every ZIP code in Idaho, we tested whether the ZIP centroid falls inside; if so, its population counts. We then divide by Idaho’s total population to produce the percentage. The full methodology for all 50 states is on the hub page.
Suggested citation: SimpleMapLab (2026). 100 Miles Around Boise: How Much of Idaho Is Inside? Part of the State Capital Radius study. Retrieved from https://www.simplemaplab.com/studies/state-capital-radius/idaho. Licensed under CC-BY 4.0.