How much flood risk does Sioux County actually carry?
Sioux County lands at the 10th percentile of FEMA's National Risk Index for flooding, "Very Low" territory — among the lowest flood hazard in the country — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about once every 2 years. County-wide, not parcel-specific: FEMA's real flood-zone map is queried live, never shipped as a download.
Sioux County's flood-insurance compliance gap
Homes with a federally backed mortgage inside Sioux 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, 0% of them do — 0 active policies against 4 structures FEMA counts in that zone, leaving a real compliance gap. Across all residential structures in Sioux County, not just the ones FEMA mandates, 0.3% 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 2849 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 2906 of 3144 by population (1 is biggest). About 3,713 people live in Sioux County, North Dakota, spread over 1,094.052 square miles.
What to do next if you own or are buying in Sioux County
Across all of Sioux County's 1,098 residential structures, 3 carry an NFIP policy today — a county-wide count that still can't tell you one address's own mapped zone.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Sioux County's numbers. The guide to what the Special Flood Hazard Area actually means explains why the mandatory-insurance rule exists and who it applies to.