Total bridges
570
Public highway bridges in Iroquois County
County profile · official public datasets
Iroquois County, IL
570 public highway bridges tracked in the FHWA National Bridge Inventory: 46.5% rated Good, 39.1% Fair, 14.4% Poor.
- 570
- Public bridges
- 46.5%
- Good condition
- 14.4%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Iroquois County posts a higher-than-median Poor-condition share among rated counties in the state across large county bridge inventory.
- 90th
- of 102 on Poor share
- 14.4%
- Poor-condition share
- 570
- public highway bridges
- 1980
- 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.
Iroquois County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Iroquois County ranks #90 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 14.4%). Iroquois County, Illinois contains 570 public highway bridges. Roughly 46.5% are rated “Good,” 39.1% “Fair,” and 14.4% “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
46.5%
265 of 570 rated 7-9
Fair condition
39.1%
223 of 570 rated 5-6
Poor condition
14.4%
82 of 570 rated 4 or below
In-state Poor-share rank
#90 of 102
Among Illinois counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 570 NBI-tracked bridges by lowest applicable component rating.
Good 46.5% (265)
Fair 39.1% (223)
Poor 14.4% (82)
Iroquois County's Poor-condition bridges carry 75,495 vehicle crossings a day
That is 16.1% of the county's reported daily bridge traffic on 14.4% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 921 crossings a day against 395 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 569 of 570 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
34.2% of Iroquois County's bridges have passed the 50-year mark
195 of the 570 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 46.5% 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 12% of the county's Poor-condition bridge traffic
FAI-57 NB over IC RR, built 1967, carries 9,050 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 82-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 75,495 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Iroquois County's bridges were built
570 bridges with a recorded construction year, grouped by decade
- pre-1900 1
Built before 1900
1 bridges
- 1900s 5
1900–1909
5 bridges
- 1910s 15
1910–1919
15 bridges
- 1920s 15
1920–1929
15 bridges
- 1930s 14
1930–1939
14 bridges
- 1940s 3
1940–1949
3 bridges
- 1950s 33
1950–1959
33 bridges
- 1960s
1960–1969
83 bridges
- 1970s
1970–1979
81 bridges
- 1980s
1980–1989
115 bridges
- 1990s
1990–1999
81 bridges
- 2000s
2000–2009
68 bridges
- 2010s 44
2010–2019
44 bridges
- 2020s 12
2020–2029
12 bridges
What this shows Construction peaked in the 1980s, when 115 of the county's bridges still in the inventory were built, which is 20.2% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year (1980) matches the Illinois average (1979).
How Iroquois County compares with Illinois's closest counties by inventory size
The 5 Illinois counties nearest Iroquois County in number of bridges, with their condition splits. Its 14.4% Poor share is the 6th-lowest of these 6. Its average build year of 1980 against a peer-group mean of 1979 is in line with the group.
Showing the 5 closest of 101 Illinois counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| McLean County | 624 | 60.9% | 36.2% | 2.9% | 1981 |
| Livingston County | 579 | 51.8% | 39.9% | 8.3% | 1978 |
| Iroquois County (this page) | 570 | 46.5% | 39.1% | 14.4% | 1980 |
| LaSalle County | 528 | 39.4% | 48.3% | 12.3% | 1978 |
| Madison County | 523 | 49.3% | 42.3% | 8.4% | 1979 |
| Vermilion County | 494 | 27.7% | 65% | 7.3% | 1979 |
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 Iroquois 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 Iroquois County, both outside Illinois so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside IL (570 bridges here).
- York County, PA · 569 bridges
- Reno County, KS · 573 bridges
- Linn County, OR · 566 bridges
- Prince George's County, MD · 576 bridges
Similar average build year
Nearest mean year-built outside IL (1980 here).
- Tulsa County, OK · avg 1980 · 1,135 bridges
- Miami-Dade County, FL · avg 1980 · 1,057 bridges
- Pulaski County, AR · avg 1980 · 721 bridges
- McLennan County, TX · avg 1980 · 714 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
All bridges (570)
DANFORTH RD FAS 33
PoorOver: I-57
4.59 MI S OF ILL 116, Iroquois, IL
Built 1967 Load: 30.5 t ADT: 200
US 45-52
PoorOver: LANGAN CR
5.15 MI N OF US 52-IL 49, Iroquois, IL
Built 1952 Load: 31.1 t ADT: 3,650
TR 345B
PoorOver: TRIB LITTLE MUD CK
4MI W CISSNA PARK, Iroquois, IL
Built 1920 Load: 31.1 t ADT: 50
FAI-57 NB
PoorOver: IC RR
8.98 MI S ASHKUM INT, Iroquois, IL
Built 1967 Load: 32.4 t ADT: 9,050
FAS-330 CH31
PoorOver: IROQUOIS RIVER
1MI N WATSEKA ON 31, Iroquois, IL
Built 1965 Load: 32.4 t ADT: 1,200
ILL 54
PoorOver: I 57
ONARGA INTERCHANGE, Iroquois, IL
Built 1967 Load: 32.7 t ADT: 1,150
TR 94A
PoorOver: TRIB. TO SPRING CR
2 MI E. 45&24-.25 N, Iroquois, IL
Built 1928 Load: 33.0 t ADT: 25
TR 1
PoorOver: FOUNTAIN CR
1.5 MI N EAST LYNN, Iroquois, IL
Built 1958 Load: 33.0 t ADT: 50
FAS 321 (CH 4)
PoorOver: I-57
CLIFTON INTER, Iroquois, IL
Built 1965 Load: 34.7 t ADT: 825
FAI-57 SB
PoorOver: WEST SECOND ST
8.6 MI S ASHKUM INT, Iroquois, IL
Built 1967 Load: 35.6 t ADT: 9,050
TR 331A
PoorOver: STREAM
0.8 MI. E. CH 41, Iroquois, IL
Built 1976 Load: 35.6 t ADT: 75
TR 4
PoorOver: STREAM
0.3 MI N THAWVILLE, Iroquois, IL
Built 1980 Load: 36.0 t ADT: 50
TR 41
PoorOver: LANGAN CREEK
3W 0.5S OF CLIFTON, Iroquois, IL
Built 1985 Load: 36.6 t ADT: 50
TR 104
PoorOver: TRIB PRAIRIE CREEK
2MI E1.5MI N DANFORT, Iroquois, IL
Built 1976 Load: 37.6 t ADT: 75
TR 317
PoorOver: UNNAMED TRIBUTARY
2.25 M W STOCKLAND, Iroquois, IL
Built 1995 Load: 37.6 t ADT: 50
US 45 & US 52
PoorOver: PRAIRIE CREEK
1.33 MI N OF US 52-IL 49, Iroquois, IL
Built 1952 Load: 38.9 t ADT: 3,250
FAS 334 /C.H.9
PoorOver: FAI 57
BUCKLEY INTERCHANGE, Iroquois, IL
Built 1968 Load: 40.2 t ADT: 1,050
TR 155
PoorOver: PRAIRE CREEK
2 MI N US RTE 24&CH8, Iroquois, IL
Built 1976 Load: 40.8 t ADT: 75
FAI-57 SB
PoorOver: Louis Creek
7.33 M S ONARGA INT, Iroquois, IL
Built 1968 Load: 43.1 t ADT: 8,750
FAI 57 NB
PoorOver: Louis Creek
7.33 M S ONARGA INT, Iroquois, IL
Built 1968 Load: 43.7 t ADT: 8,750
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.