County profile · official public datasets

Dewey County, SD

28 public highway bridges tracked in the FHWA National Bridge Inventory: 57.1% rated Good, 28.6% Fair, 14.3% Poor.

28
Public bridges: 57.1%
Good condition: 14.3%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Dewey County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 47%
lowest Poor share in state: 14.3%
Poor-condition share: 28
public highway bridges: 1986
avg year built

Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.

Dewey County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Dewey County ranks #31 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 14.3%). Dewey County, South Dakota contains 28 public highway bridges. Roughly 57.1% are rated “Good,” 28.6% “Fair,” and 14.3% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.

Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.

Source: FHWA National Bridge Inventory. See methodology for full definitions.

Total bridges

Public highway bridges in Dewey County

Good condition

57.1%

16 of 28 rated 7-9

Fair condition

28.6%

8 of 28 rated 5-6

Poor condition

14.3%

4 of 28 rated 4 or below

In-state Poor-share rank

#31 of 66

Among South Dakota counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 28 NBI-tracked bridges by lowest applicable component rating.

Good

57.1% (16)

Fair

28.6% (8)

Poor

14.3% (4)

Dewey County's Poor-condition bridges carry 458 vehicle crossings a day

That is 5.2% of the county's reported daily bridge traffic on 14.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 115 crossings a day against 437 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.

Computed over the 28 of 28 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

42.9% of Dewey County's bridges have passed the 50-year mark

12 of the 28 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 57.1% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.

Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.

One structure carries 39.3% of the county's Poor-condition bridge traffic

IRR BIA RTE 2 over RED WATER CREEK, built 1961, carries 180 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 4-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 458 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1950s

1
1960s

10
1970s

1
1980s

2
1990s

4
2000s

4
2010s

4
2020s

2

What this shows Construction peaked in the 1960s, when 10 of the county's bridges still in the inventory were built, which is 35.7% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1986, 11 years newer than the South Dakota average of 1975.

How Dewey County compares with South Dakota's closest counties by inventory size

The 5 South Dakota counties nearest Dewey County in number of bridges, with their condition splits. Its 14.3% Poor share is the 5th-lowest of these 6. Its average build year of 1986 against a peer-group mean of 1977 is 9 years newer.

Showing the 5 closest of 65 South Dakota counties eligible for comparison.

Bridge inventory size and condition shares for Dewey County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Sully County	31	45.2%	35.5%	19.4%	1979
Ziebach County	30	26.7%	63.3%	10%	1969
Mellette County	28	32.1%	60.7%	7.1%	1980
Dewey County (this page)	28	57.1%	28.6%	14.3%	1986
Buffalo County	25	32%	64%	4%	1976
Potter County	24	54.2%	45.8%	0%	1981

Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Dewey County's. Source: FHWA National Bridge Inventory, 2024 release.

Nationwide counties with similar inventory size or average build year

Two NBI-derived peer sets for Dewey County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (28 bridges here).

Crowley County, CO · 28 bridges
Dolores County, CO · 28 bridges
Lafayette County, FL · 28 bridges
Union County, FL · 28 bridges

Similar average build year

Nearest mean year-built outside SD (1986 here).

El Paso County, TX · avg 1986 · 783 bridges
Caddo County, LA · avg 1986 · 682 bridges
Weld County, CO · avg 1986 · 614 bridges
Polk County, IA · avg 1986 · 545 bridges

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 28 Good 16 Fair 8 Poor 4

All bridges (28)

Sort:

IRR STATE PARK RD

Fair

Over: LITTLE MOREAU RV

5.7S .3W TIMBER LK, Dewey, SD

Built 1950 Load: 10.9 t ADT: 5

IRR BIA RTE 7

Fair

Over: MOREAU RIVER

.7 KM NORTH OF PROMISE, Dewey, SD

Built 1961 Load: 16.7 t ADT: 105

IRR BIA RTE 2

Fair

Over: LITTLE MOREAU CREEK

3.2 KM W OF WHITE HORSE, Dewey, SD

Built 1960 Load: 18.1 t ADT: 109

IRR BIA RTE 7

Fair

Over: BEAVER CREEK

7.2 KM EAST OF PROMISE, Dewey, SD

Built 1960 Load: 24.5 t ADT: 100

IRR COUNTY ROAD

Fair

Over: Creek

7.0W 9.0S TIMBER LK, Dewey, SD

Built 1960 Load: 24.9 t ADT: 38

IRR SD063

Fair

Over: MOREAU RV

13 N JCT US 212, Dewey, SD

Built 1971 Load: 25.5 t ADT: 767

IRR COUNTY ROAD

Fair

Over: Creek

1.7 W 5.2 N LANTRY, Dewey, SD

Built 1965 Load: 28.4 t ADT: 55

IRR BIA RTE 3

Fair

Over: HAND BOY CREEK

3.2KM W OF RTE 7 JUNCTION, Dewey, SD

Dewey County Bridge Snapshot

Condition distribution

Dewey County's Poor-condition bridges carry 458 vehicle crossings a day

42.9% of Dewey County's bridges have passed the 50-year mark

One structure carries 39.3% of the county's Poor-condition bridge traffic

How Dewey County compares with South Dakota's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

All bridges (28)

IRR STATE PARK RD

IRR BIA RTE 7

IRR BIA RTE 2

IRR BIA RTE 7

IRR COUNTY ROAD

IRR SD063

IRR COUNTY ROAD

IRR BIA RTE 3

BIA Highway 4

IRR COUNTY ROAD

IRR BIA RTE 7

IRR BIA RTE 4

IRR BIA ROUTE 8

IRR BIA RTE 8

IRR BIA RTE 3

IRR COUNTY ROAD

IRR US212

IRR US212

IRR US212

IRR BIA RTE 7

IRR BIA RTE 3

IRR SD020

IRR SD020

IRR SD020

FAS 6247

IRR BIA RTE 7

IRR BIA RTE 7

IRR BIA RTE 2

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