How much flood risk does Sioux County actually carry?
Sioux County lands at the 49.5th percentile of FEMA's National Risk Index for flooding, "Relatively Low" territory — below the national norm for flood hazard — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 3.3 times a year. 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
Sioux County is one of the counties where FEMA's own denominator for mandated flood-zone structures is missing, so no compliance rate is shown rather than a guessed one — the data quality guide covers how common this is. Across all residential structures in Sioux County, not just the ones FEMA mandates, 1.2% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
Where Sioux County ranks
Sioux County sits at rank 1648 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 1281 of 3144 by population (1 is biggest). About 36,554 people live in Sioux County, Iowa, spread over 767.911 square miles.
Checking a specific address in Sioux County
FEMA counts 12,153 residential structures in Sioux County overall, 151 of them carrying some form of NFIP coverage — but a lender or insurer cares about one parcel, not that county total.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Sioux County's numbers. See the data quality guide for why Sioux County, like hundreds of other counties, doesn't get a clean compliance percentage.