Ada County, ID flood risk explained
Flood hazard in Ada County sits at the 89.8th national percentile, a middling flood hazard by national standards; driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about once every 1 years. That's a county-wide figure, not a per-address one — FEMA's parcel maps are a live lookup, not a bulk file.
Who actually carries the flood insurance FEMA requires
Homes with a federally backed mortgage inside Ada County's mapped high-risk flood zone (the Special Flood Hazard Area, or SFHA) are legally required to carry an NFIP flood policy. In practice, 25.2% of them do — 968 active policies against 3,840 structures FEMA counts in that zone, leaving a real compliance gap. Looking beyond the mandated zone, 0.9% of all residential structures in Ada County carry flood coverage voluntarily or otherwise — relevant because most NFIP claims nationally come from outside the mapped SFHA.
Ada County against the rest of the country
Among the 3144 US counties FEMA scores for flood hazard, Ada County ranks 337 — 1 being the highest hazard nationally — and 138 by population among all 3144 counties covered here, where 1 is the largest. Ada County, Idaho is home to about 535,799 people across 1,052.252 square miles of land.
Your street may differ from Ada County's average
Across all of Ada County's 163,202 residential structures, 1,541 carry an NFIP policy today — a county-wide count that still can't tell you one address's own mapped zone.
Where Ada County's figures come from
Every figure on this page traces to a named FEMA dataset, documented in the methodology guide. If you're unsure why any of this insurance requirement exists at all, the SFHA explainer covers it from first principles.