County profile · official public datasets

Clay County, SD

94 public highway bridges tracked in the FHWA National Bridge Inventory: 58.5% rated Good, 25.5% Fair, 16% Poor.

94
Public bridges: 58.5%
Good condition: 16%
Poor condition

The verdict

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

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

36th
of 66 on Poor share: 16%
Poor-condition share: 94
public highway bridges: 1985
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.

Clay County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Clay County ranks #36 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 16%). Clay County, South Dakota contains 94 public highway bridges. Roughly 58.5% are rated “Good,” 25.5% “Fair,” and 16% “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 Clay County

Good condition

58.5%

55 of 94 rated 7-9

Fair condition

25.5%

24 of 94 rated 5-6

Poor condition

16%

15 of 94 rated 4 or below

In-state Poor-share rank

#36 of 66

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

Condition distribution

Share of 94 NBI-tracked bridges by lowest applicable component rating.

Good

58.5% (55)

Fair

25.5% (24)

Poor

16% (15)

Clay County's Poor-condition bridges carry 1,690 vehicle crossings a day

That is 3.8% of the county's reported daily bridge traffic on 16% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 113 crossings a day against 539 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 94 of 94 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

26.6% of Clay County's bridges have passed the 50-year mark

25 of the 94 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 58.5% 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 32.5% of the county's Poor-condition bridge traffic

700 S. DAKOTA AVE. over VERMILLION RV, built 1975, carries 550 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 15-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,690 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

2
1910s

1
1920s

1
1930s

8
1940s

4
1960s

4
1970s

11
1980s

10
1990s

18
2000s

21
2010s

9
2020s

5

What this shows Construction peaked in the 2000s, when 21 of the county's bridges still in the inventory were built, which is 22.3% of those with a recorded year. That cohort is now 15 to 24 years old in the 2024 inventory. Its average build year is 1985, 10 years newer than the South Dakota average of 1975.

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

The 5 South Dakota counties nearest Clay County in number of bridges, with their condition splits. Its 16% Poor share is the 5th-lowest of these 6. Its average build year of 1985 against a peer-group mean of 1976 is 9 years newer.

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

Bridge inventory size and condition shares for Clay County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Yankton County	99	41.4%	43.4%	15.2%	1983
McCook County	98	44.9%	44.9%	10.2%	1977
Custer County	95	46.3%	48.4%	5.3%	1977
Clay County (this page)	94	58.5%	25.5%	16%	1985
Tripp County	90	27.8%	44.4%	27.8%	1975
Jackson County	89	29.2%	55.1%	15.7%	1969

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 Clay 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 Clay County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (94 bridges here).

Yukon-Koyukuk County, AK · 94 bridges
Lee County, AR · 94 bridges
Huerfano County, CO · 94 bridges
Henry County, KY · 94 bridges

Similar average build year

Nearest mean year-built outside SD (1985 here).

Hillsborough County, FL · avg 1985 · 840 bridges
Lancaster County, NE · avg 1985 · 661 bridges
Nueces County, TX · avg 1985 · 528 bridges
Grayson County, TX · avg 1985 · 513 bridges

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

All 94 Good 55 Fair 24 Poor 15

All bridges (94)

Sort:

Clay County Bridge Snapshot

Condition distribution

Clay County's Poor-condition bridges carry 1,690 vehicle crossings a day

26.6% of Clay County's bridges have passed the 50-year mark

One structure carries 32.5% of the county's Poor-condition bridge traffic

How Clay 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 (94)

SD019

SD019

SD019

45206 BLUFF RD

30940 BLUFF ROAD

29970 457 AVE.

30440 452 AVE

SD050

31080 459 AVE.

SD019

46030 312 ST.

SD019

46340 304 ST.

46010 302 ST.

30730 452 AVE

SD019

SD019

SD019

30370 461 AVE

30880 UNIVER. ROAD

SD046

45920 299 ST.

30260 463 AVE.

SD046

NORWEFIAN AVE.

30020 458 AVE.

45860 300TH ST

SD046

302 ST.

46080 314 ST.

46530 314TH ST.

46540 307TH ST.

29830 ASH CRK AVE.

46580 313 ST.

29810 466 ST.

45980 303 ST.

46380 308 ST

46610 305TH ST.

46600 313 ST.

46080 313 ST.

45530 306 STREET

46320 306 ST.

31160 UNIVER. ROAD

700 S. DAKOTA AVE.

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