Blog · October 14, 2026 · South Dakota
Sully County Flood Zone Map: checking a property's flood zone
Flood zones are set by FEMA, and checking one near Onida takes a few minutes.
Main page: Sully County, SD GIS & Parcel Viewer (official map link, county facts and neighboring maps).
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Before you buy or build near Cow Creek, check the Sully County flood zone map: the zone on that map shapes insurance, building rules and resale. What this Sully County guide covers: finding the address on FEMA's map, decoding A, AE and X, and pairing it with the District III regional GIS map.
Getting started with the Sully County flood zone map
If you'd rather pan and zoom, open the National Flood Hazard Layer viewer, which draws the zones over aerial imagery, and that holds around Missouri River too. A tract near Onida without an address is still easy to locate: zoom in from the nearest road then click the parcel area.
Opening the official parcel viewer
Your first stop is the District III regional GIS map; it covers every tax parcel in the county, Onida included. If you only know roughly where the land is, zoom in from Cow Creek and click the parcel itself. If the land is near Onida, copy the parcel ID before closing the panel; every records desk in the county will want it.
Where the recorded documents are
For anything that matters, pull the recorded deed through the Register of Deeds; the viewer just points to it, and that holds around Agar too. On ground around Cow Creek, use the book and page from the tax record so staff can find the deed fast.
Reading A, AE and X
In and around Agar, any A or V zone are Special Flood Hazard Areas, which FEMA defines as a 1% annual chance of flooding. Closer to Cow Creek, a shaded X area is moderate risk, between the 1% and 0.2% annual chance floods; unshaded X means minimal mapped risk.
Which office to call
Deeds, mortgages and recorded plats for land near Onida sit in the index kept by the Register of Deeds, often with an online index. Building or septic questions for a lot near Agar go to planning, building or health offices, and the answer depends on jurisdiction.
Places you'll see on the map
Onida holds the county offices, which is where the courthouse records live. Smaller places on the map include Agar, Cow Creek, and Missouri River. About 1,494 people live in Sully County (Census estimate, 2023) spread over about 1,007 square miles. Features like Missouri River help you orient on the aerial around Missouri River.
A short flood checklist
For a parcel near Onida, ask the seller whether the home has flooded before closing; getting a quote early avoids surprises.
A word on accuracy
With a lot near Cow Creek, acreage on the record is an assessed number; only a licensed surveyor sets the real boundary on the ground. If the land is near Onida, owner names and values update on a schedule, so a deed recorded last month can take weeks to appear.
When a parcel crosses a boundary
Sully County touches Dewey County, Hughes County, Hyde County, Potter County, and Stanley County; every one of them runs a separate parcel map. A tract near the line by Onida can be split across two assessors' files, so look at the adjacent map before you assume the acreage. For a parcel near Agar, our state page links each bordering county map for South Dakota.
Use the county map alongside FEMA
FEMA doesn't draw property lines, so check the District III regional GIS map too to confirm you have the right parcel near Agar.
Insurance, lenders and building
If a building sits in a Special Flood Hazard Area and the loan is federally backed or regulated, flood insurance is generally required where the community participates in the National Flood Insurance Program, which applies near Cow Creek as much as anywhere. Building or adding on near Onida in a mapped zone can trigger elevation rules; check with the county or town building office early.
Using it on a phone
The parcel map usually runs in a mobile browser, which helps when you're standing on land near Onida, though signal can drop in rural spots. A saved image of the lot near Agar and its lines helps when you meet an owner or agent.
Low spots and local drainage
Low-lying fields near Agar may not have detailed mapping, so look for water marks and debris lines. Wetlands near Agar can limit building even outside a flood zone; the National Wetlands Inventory mapper shows mapped wetlands.
Frequently asked
Is my property near Missouri River in a flood zone?
Usually, FEMA's free map shows the zone for any spot near Cow Creek, and the zone code appears on the map.
Do I need to worry about flooding in Zone X around Onida?
It depends, but X zones around Onida are lower risk, not no risk, and floods still happen outside high-risk zones.
Will my lender require flood insurance near Missouri River?
If you're looking near Missouri River, it's typically required only for structures in high-risk zones with federally backed loans, in communities that take part in the NFIP.
What is a base flood elevation around Agar?
If you're looking near Missouri River, the base flood elevation is the water level expected in the 1% annual chance flood; local rules may require building above it.
How do I save a parcel from the viewer in Sully County?
For acreage around Cow Creek, some viewers offer PDF export; downloads of raw data vary by county.
Open the official Sully County, SD parcel map See it in the Platbookmapper directory
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey, especially for fences, setbacks, or boundary disputes.