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.

Total bridges

570

Public highway bridges in Iroquois County

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.

pre-1900

1
1900s

5
1910s

15
1920s

15
1930s

14
1940s

3
1950s

33
1960s

83
1970s

81
1980s

115
1990s

81
2000s

68
2010s

44
2020s

12

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.

Bridge inventory size and condition shares for Iroquois County and the 5 Illinois counties closest to it in inventory size
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 570 Good 265 Fair 223 Poor 82

All bridges (570)

Sort:

Iroquois County Bridge Snapshot

Condition distribution

Iroquois County's Poor-condition bridges carry 75,495 vehicle crossings a day

34.2% of Iroquois County's bridges have passed the 50-year mark

One structure carries 12% of the county's Poor-condition bridge traffic

How Iroquois County compares with Illinois'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 (570)

TR 77

TR 31

FAS 335 CH 10

TR 313

TR 61

TR 422

TR 95

TR 363A

FAS 335W/CH 10

TR 89

TR 22B

TR 164

TR 374

TR 170

TR 442

TR 290

TR 363

TR 178

TR 458

TR 189

CH 2

CH 29

FAI-57 SB

FAI-57 NB

FAI-57 SB

US 24

TWP RD 49A

FAI-57

US 45

FAI-57

TR 269

TR 307

TR 269A

TR 36

TR 292

TR 2B

TR 319A

TR 200

TR 114

TR 57

TR 58

CH 15

TR 344

TR 368

TR 19

TR 251

TR 288

TR 5

TR 140

TR 188

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