Total bridges
51
Public highway bridges in Gregory County
County profile · official public datasets
Gregory County, SD
51 public highway bridges tracked in the FHWA National Bridge Inventory: 39.2% rated Good, 54.9% Fair, 5.9% Poor.
- 51
- Public bridges
- 39.2%
- Good condition
- 5.9%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Gregory County posts a top-quartile lowest Poor-condition share among rated counties in the state across rated county bridge inventory.
- Top 17%
- lowest Poor share in state
- 5.9%
- Poor-condition share
- 51
- public highway bridges
- 1976
- 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.
Gregory County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Gregory County ranks #11 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.9%). Gregory County, South Dakota contains 51 public highway bridges. Roughly 39.2% are rated “Good,” 54.9% “Fair,” and 5.9% “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.
Good condition
39.2%
20 of 51 rated 7-9
Fair condition
54.9%
28 of 51 rated 5-6
Poor condition
5.9%
3 of 51 rated 4 or below
In-state Poor-share rank
#11 of 66
Among South Dakota counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 51 NBI-tracked bridges by lowest applicable component rating.
Good 39.2% (20)
Fair 54.9% (28)
Poor 5.9% (3)
Gregory County's Poor-condition bridges carry 235 vehicle crossings a day
That is 2.8% of the county's reported daily bridge traffic on 5.9% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 78 crossings a day against 174 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 51 of 51 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
49% of Gregory County's bridges have passed the 50-year mark
25 of the 51 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 39.2% 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 80.4% of the county's Poor-condition bridge traffic
354 AVENUE over PONCA CK, built 1952, carries 189 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 3-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 235 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Gregory County's bridges were built
51 bridges with a recorded construction year, grouped by decade
- 1920s 1
1920–1929
1 bridges
- 1930s 2
1930–1939
2 bridges
- 1940s 3
1940–1949
3 bridges
- 1950s
1950–1959
8 bridges
- 1960s
1960–1969
7 bridges
- 1970s
1970–1979
8 bridges
- 1980s
1980–1989
6 bridges
- 1990s
1990–1999
4 bridges
- 2000s
2000–2009
8 bridges
- 2010s 2
2010–2019
2 bridges
- 2020s 2
2020–2029
2 bridges
What this shows Construction peaked in the 1950s, when 8 of the county's bridges still in the inventory were built, which is 15.7% of those with a recorded year. That cohort is now 65 to 74 years old in the 2024 inventory. Its average build year (1976) matches the South Dakota average (1975).
How Gregory County compares with South Dakota's closest counties by inventory size
The 5 South Dakota counties nearest Gregory County in number of bridges, with their condition splits. Its 5.9% Poor share is the 2nd-lowest of these 6. Its average build year of 1976 against a peer-group mean of 1973 is in line with the group.
Showing the 5 closest of 65 South Dakota counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Sanborn County | 53 | 34% | 49.1% | 17% | 1974 |
| Gregory County (this page) | 51 | 39.2% | 54.9% | 5.9% | 1976 |
| Corson County | 49 | 32.7% | 57.1% | 10.2% | 1973 |
| Harding County | 49 | 51% | 46.9% | 2% | 1985 |
| 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 Gregory 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 Gregory County, both outside South Dakota so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside SD (51 bridges here).
- Jackson County, KY · 51 bridges
- Arecibo County, PR · 51 bridges
- Naguabo County, PR · 51 bridges
- San Lorenzo County, PR · 51 bridges
Similar average build year
Nearest mean year-built outside SD (1976 here).
- Marion County, IN · avg 1976 · 958 bridges
- Mohave County, AZ · avg 1976 · 641 bridges
- Comanche County, OK · avg 1976 · 593 bridges
- Prince George's County, MD · avg 1976 · 576 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
All bridges (51)
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.