🗺️Research & Data

The U.S. Septic Failure Risk Index

We scored 2,390 counties on the two things that drive septic failure — soil and system age — using USDA and Census data. SepticTankHub Research, Report #1.

🛰️USDA + Census data📍2,390 counties🔓Free to cite
🗺️ By the SepticTankHub Research team · Data as of 2026-07-08

Two things decide whether a septic system is likely to fail: the soil it drains into and the age of the system. We combined USDA soil-suitability ratings with Census housing-age data to score 2,390 counties across 31 states. The single riskiest place in America for a septic system is Pawnee County, Nebraska (risk 94/100) — and the highest-risk counties cluster where poor clay soils meet aging farmhouses: the rural Great Plains and Midwest.

The headline numbers

#1

Pawnee County, Nebraska has the highest septic failure risk in the nation (score 94/100): 94.8% poorly-suited soil and a median home built in 1945.

Source: USDA + Census# Link
76.9

Iowa has the highest average county risk score (76.9/100) of any well-covered state.

Source: SepticTankHub Research# Link
34.4

Texas has the lowest average county risk (34.4/100) of the well-covered states — better soil and newer housing.

Source: SepticTankHub Research# Link
59/100

The average scored county has a septic failure risk of 59 out of 100 — a reminder that challenging conditions are the norm, not the exception.

Source: SepticTankHub Research# Link

Septic failure risk by state

Average county risk score, for the 31 states with county-level soil coverage. Darker = higher risk.

West
WA
—
OR
—
CA
—
NV
—
ID
—
MT
—
WY
—
UT
—
CO
—
AZ
—
NM
—
AK
—
HI
—
Midwest
ND
65.6
SD
71.4
NE
73.2
KS
70.7
MN
62.3
IA
76.9
MO
69.4
WI
62.3
IL
67.8
IN
65.6
MI
74.2
OH
50.1
South
TX
34.4
OK
51.8
AR
45.6
LA
38.5
MS
64.3
AL
58.3
TN
54.5
KY
—
WV
—
VA
59.2
NC
57.2
SC
53.9
GA
—
FL
59.4
MD
59.6
DE
49
DC
—
Northeast
PA
74.2
NY
51.9
NJ
72.7
CT
—
RI
—
MA
62.4
VT
70.7
NH
62.6
ME
—
Avg risk (0–100):lowhigh
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The 100 highest-risk counties

Ranked by risk score. “Soil” = % of the county's soils rated “Very Limited” for septic; “Built” = median year homes were built. Search for your state's abbreviation.

Highest-risk US counties for septic failure — SepticTankHub Research 2026
#CountyStateRisk /100 ▼Soil %Built
1Pawnee CountyNE9494.8%1945
2Republic CountyKS9389.2%1941
3Lincoln CountyKS9083.8%1938
4Stafford CountyKS9096.5%1952
5Edwards CountyKS9089.3%1945
6Richardson CountyNE9089.1%1945
7Taylor CountyIA8995.5%1952
8Elk CountyKS8998.3%1955
9Boyd CountyNE8992.1%1950
10Jefferson CountyNE8991.1%1949
11Worth CountyIA8889.9%1949
12Audubon CountyIA8890.9%1950
13Morris CountyKS8896.1%1955
14Gogebic CountyMI8793.1%1954
15Schuylkill CountyPA8783.3%1944
16Lackawanna CountyPA8794.6%1955
17Page CountyIA8790.6%1951
18Greenwood CountyKS8797.5%1958
19Montgomery CountyKS8795.5%1956
20Jewell CountyKS8778.5%1938
21Pratt CountyKS8794.3%1955
22Rice CountyKS8794.3%1955
23Johnson CountyNE8793.5%1953
24Sanborn CountySD8792%1952
25Worth CountyMO8697.5%1959
26Montgomery CountyIA8693.1%1955
27Keokuk CountyIA8691.5%1953
28Fayette CountyIA8691%1953
29Adams CountyIA8692.8%1954
30Chase CountyKS8695.9%1958
31Kingman CountyKS8695.5%1957
32Nuckolls CountyNE8683.8%1947
33Cortland CountyNY8597.6%1961
34Houghton CountyMI8596.3%1959
35Venango CountyPA8596.5%1959
36Cambria CountyPA8592.9%1956
37Passaic CountyNJ8593.1%1956
38Howard CountyIA8590.8%1954
39Lee CountyIA8595.3%1959
40Cass CountyIA8590.9%1954
41Wapello CountyIA8594.5%1958
42Woodson CountyKS8597.8%1960
43Bourbon CountyKS8594.5%1958
44Marion CountyKS8593.1%1957
45Neosho CountyKS8596.7%1960
46Washington CountyKS8591.3%1954
47Nemaha CountyNE8591.9%1955
48McPherson CountyNE8593.9%1957
49Kings CountyNY8476.2%1943
50Fayette CountyPA8494%1958
51Lincoln CountyMN8494.7%1960
52Pipestone CountyMN8493.8%1958
53Grundy CountyMO8498.3%1962
54Washington CountyIA8497.7%1962
55Adair CountyIA8493.4%1958
56Tama CountyIA8491.8%1956
57Cloud CountyKS8487.7%1953
58Labette CountyKS8495%1959
59Dickinson CountyKS8490.9%1956
60Thomas CountyNE8491.5%1957
61Thayer CountyNE8485.9%1952
62Hooker CountyNE8493.8%1959
63Franklin CountyNE8477.2%1943
64Grant CountyNE8496.9%1961
65Douglas CountySD8492.5%1957
66Jerauld CountySD8489.3%1955
67Allegany CountyNY8398.9%1965
68Iron CountyMI8395.9%1962
69Calhoun CountyMI8395.1%1961
70Ontonagon CountyMI8395.7%1962
71Beaver CountyPA8391.8%1958
72Allegheny CountyPA8390.3%1957
73Lawrence CountyPA8390.5%1957
74Northumberland CountyPA8388%1955
75Luzerne CountyPA8393.4%1959
76Mower CountyMN8390.1%1957
77Knox CountyMO8398%1964
78Schuyler CountyMO8397.6%1963
79Cass CountyIN8388.9%1955
80Des Moines CountyIA8391.8%1958
81Butler CountyIA8389.5%1956
82Union CountyIA8394.3%1961
83Mitchell CountyIA8390%1956
84Louisa CountyIA8395.6%1962
85Clinton CountyIA8391.1%1958
86Anderson CountyKS8395.8%1962
87Chautauqua CountyKS8394.5%1960
88Blaine CountyNE8393.2%1959
89Brown CountyNE8395.7%1962
90Bay CountyMI8293.8%1962
91Crawford CountyPA8298.4%1966
92Somerset CountyPA8294.9%1963
93Armstrong CountyPA8292.4%1960
94Jefferson CountyPA8294%1962
95Linn CountyMO8297.7%1965
96Sullivan CountyMO8298.2%1965
97Franklin CountyMA8293.1%1961
98Rush CountyIN8285.1%1954
99Union CountyNJ8287%1956
100Cherokee CountyIA8287%1956

100 of 100 rows · click a column to sort · click a row name to link it

Showing the 100 highest-risk counties of 2,390 scored. Full dataset available on request.

How the score works

The risk score is 60% soil + 40% system age. Soil comes from USDA's septic soil-suitability rating — the share of a county's soils that are “Very Limited” for a conventional drain field. Age comes from the Census median year homes were built, on the logic that an older housing stock means older septic systems installed under weaker codes. Neither factor alone predicts failure, but together they map where conditions stack the deck. What you control — regular pumping and maintenance — still matters most for your specific system.

Cite this index

SepticTankHub Research. “The U.S. Septic Failure Risk Index” (Report #1), 2026, from USDA SSURGO + Census ACS data. https://www.septictankhub.com/blog/septic-failure-risk-map/. Free to republish with attribution and a link.

Methodology & sources

Methodology & Sources — data as of 2026-07-08

Risk score (0–100) = 0.6 × (% of county soils rated 'Very Limited' for septic, USDA SSURGO) + 0.4 × ageRisk, where ageRisk = clamp((2000 − median year built) / 60 × 100, 0, 100) from Census ACS B25035.

Rationale: septic failure risk rises with poorly-suited soil (drain fields struggle) and with older housing (older systems, pre-modern-code installs). Both are county-level federal data.

Counties are included only where BOTH inputs are available; soil and Census counties are joined on the 3-digit county FIPS code within each state.

This is a risk INDICATOR from landscape + housing data, not a prediction for any individual property. It excludes system-density/reliance (no clean county-level septic-reliance source) and local maintenance behavior.

Limitations & caveats
  • A risk INDICATOR from landscape + housing data — not a prediction for any individual property.
  • Excludes system density/reliance (no clean county-level septic-reliance source) and maintenance behavior.
  • Covers 2,390 counties in 31 states; several western/island states use non-county soil survey areas and aren't yet included.
  • State averages are shown only where at least half a state's counties are scored.
Sources

Frequently asked questions

Pawnee County, Nebraska tops our index with a risk score of 94 out of 100 — about 94.8% of its soils are poorly suited for septic and the median home was built in 1945. The highest-risk counties cluster in the rural Great Plains and Midwest, where poor clay soils meet aging housing.
It combines two federal datasets: 60% from USDA soil suitability (the share of a county's soils rated 'Very Limited' for a conventional septic drain field) and 40% from housing age (Census median year built — older homes tend to have older systems installed under weaker codes). Scores run 0–100.
Iowa has the highest average county risk (76.9), driven by poor soils and old rural housing stock. Texas has the lowest of the well-covered states (34.4).
No. This is a landscape-and-housing risk indicator, not a prediction for any individual property. A well-maintained system on a well-designed site can last decades even in a high-risk county — and regular pumping is the single biggest factor you control. It flags where conditions make failure more likely on average.
We scored 2390 counties across 31 states where county-level USDA soil surveys join cleanly to Census housing data. Several western and island states organize their soil surveys by non-county 'survey areas', so their counties aren't yet in this edition.
Pump on schedule, protect the drain field (no parking or heavy structures on it), spread out water use, and inspect before problems appear. See our cost-of-neglect analysis for why maintenance is the cheapest insurance you can buy.

This is Report #1, published 2026. Media & data inquiries: [email protected] · see our press page. Related: Soil Suitability · Cost of Neglect.