County profile · official public datasets

Corson County, SD

49 public highway bridges tracked in the FHWA National Bridge Inventory: 32.7% rated Good, 57.1% Fair, 10.2% Poor.

49
Public bridges: 32.7%
Good condition: 10.2%
Poor condition

The verdict

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

Corson County posts a better-than-median Poor-condition share among rated counties in the state across rated county bridge inventory.

Top 35%
lowest Poor share in state: 10.2%
Poor-condition share: 49
public highway bridges: 1973
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.

Corson County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Corson County ranks #23 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 10.2%). Corson County, South Dakota contains 49 public highway bridges. Roughly 32.7% are rated “Good,” 57.1% “Fair,” and 10.2% “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 Corson County

Good condition

32.7%

16 of 49 rated 7-9

Fair condition

57.1%

28 of 49 rated 5-6

Poor condition

10.2%

5 of 49 rated 4 or below

In-state Poor-share rank

#23 of 66

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

Condition distribution

Share of 49 NBI-tracked bridges by lowest applicable component rating.

Good

32.7% (16)

Fair

57.1% (28)

Poor

10.2% (5)

Corson County's Poor-condition bridges carry 2,990 vehicle crossings a day

That is 17.2% of the county's reported daily bridge traffic on 10.2% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 598 crossings a day against 223 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 49 of 49 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

59.2% of Corson County's bridges have passed the 50-year mark

29 of the 49 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 32.7% 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 46.6% of the county's Poor-condition bridge traffic

IRR US012 over CLAYMORE CK, built 1958, carries 1,392 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 5-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 2,990 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

5
1940s

1
1950s

3
1960s

16
1970s

6
1980s

5
1990s

4
2000s

6
2010s

3

What this shows Construction peaked in the 1960s, when 16 of the county's bridges still in the inventory were built, which is 32.7% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1973) matches the South Dakota average (1975).

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

The 5 South Dakota counties nearest Corson County in number of bridges, with their condition splits. Its 10.2% Poor share is the 3rd-lowest of these 6. Its average build year of 1973 against a peer-group mean of 1974 is in line with the group.

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

Bridge inventory size and condition shares for Corson County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Sanborn County	53	34%	49.1%	17%	1974
Gregory County	51	39.2%	54.9%	5.9%	1976
Harding County	49	51%	46.9%	2%	1985
Corson County (this page)	49	32.7%	57.1%	10.2%	1973
Faulk County	46	19.6%	58.7%	21.7%	1966
Douglas County	44	45.5%	38.6%	15.9%	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 Corson 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 Corson County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (49 bridges here).

Mono County, CA · 49 bridges
Yuma County, CO · 49 bridges
Calhoun County, FL · 49 bridges
Crawford County, GA · 49 bridges

Similar average build year

Nearest mean year-built outside SD (1973 here).

Jefferson County, AL · avg 1973 · 1,068 bridges
Erie County, NY · avg 1973 · 906 bridges
Davidson County, TN · avg 1973 · 832 bridges
Lancaster County, PA · avg 1973 · 801 bridges

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

All 49 Good 16 Fair 28 Poor 5

Fair-condition bridges (28)

Sort:

Corson County Bridge Snapshot

Condition distribution

Corson County's Poor-condition bridges carry 2,990 vehicle crossings a day

59.2% of Corson County's bridges have passed the 50-year mark

One structure carries 46.6% of the county's Poor-condition bridge traffic

How Corson 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

Fair-condition bridges (28)

Township Road

IRR BIA RTE 2

220TH AVENUE

230th Avenue

COUNTY ROAD

IRR SD1806

IRR SD063

IRR BIA RTE 44

IRR US012

IRR US012

IRR US012

Kenel Road

IRR US012

IRR US012

IRR US012

IRR SD1806

IRR US012

IRR SD065

IRR SD1806

IRR SD065

IRR US012

Morristown Road

IRR SD065

IRR BIA RTE 44

IRR US012

IRR SD063

Corson County 35

IRR US012

Related