Total bridges
118
Public highway bridges in Johnson County
County profile · official public datasets
Johnson County, IL
118 public highway bridges tracked in the FHWA National Bridge Inventory: 58.5% rated Good, 39% Fair, 2.5% Poor.
- 118
- Public bridges
- 58.5%
- Good condition
- 2.5%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Johnson County posts a top-5% lowest Poor-condition share among rated counties in the state across mid-size county bridge inventory.
- Top 3%
- lowest Poor share in state
- 2.5%
- Poor-condition share
- 118
- public highway bridges
- 1979
- 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.
Johnson County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Johnson County ranks #3 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 2.5%). Johnson County, Illinois contains 118 public highway bridges. Roughly 58.5% are rated “Good,” 39% “Fair,” and 2.5% “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
58.5%
69 of 118 rated 7-9
Fair condition
39%
46 of 118 rated 5-6
Poor condition
2.5%
3 of 118 rated 4 or below
In-state Poor-share rank
#3 of 102
Among Illinois counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 118 NBI-tracked bridges by lowest applicable component rating.
Good 58.5% (69)
Fair 39% (46)
Poor 2.5% (3)
Johnson County's Poor-condition bridges carry 454 vehicle crossings a day
That is 0.2% of the county's reported daily bridge traffic on 2.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 151 crossings a day against 1,186 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 117 of 118 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
42.4% of Johnson County's bridges have passed the 50-year mark
50 of the 118 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 49.6% of the county's Poor-condition bridge traffic
TR 111 over DUTCHMAN CR. TRIB., built 1978, carries 225 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 454 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Johnson County's bridges were built
118 bridges with a recorded construction year, grouped by decade
- 1900s 1
1900–1909
1 bridges
- 1920s 3
1920–1929
3 bridges
- 1930s 9
1930–1939
9 bridges
- 1940s 1
1940–1949
1 bridges
- 1950s 3
1950–1959
3 bridges
- 1960s 3
1960–1969
3 bridges
- 1970s
1970–1979
37 bridges
- 1980s
1980–1989
24 bridges
- 1990s
1990–1999
15 bridges
- 2000s 13
2000–2009
13 bridges
- 2010s 7
2010–2019
7 bridges
- 2020s 2
2020–2029
2 bridges
What this shows Construction peaked in the 1970s, when 37 of the county's bridges still in the inventory were built, which is 31.4% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1979) matches the Illinois average (1979).
How Johnson County compares with Illinois's closest counties by inventory size
The 5 Illinois counties nearest Johnson County in number of bridges, with their condition splits. Its 2.5% Poor share is the 1st-lowest of these 6. Its average build year of 1979 against a peer-group mean of 1984 is 5 years older.
Showing the 5 closest of 101 Illinois counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Kendall County | 132 | 52.3% | 35.6% | 12.1% | 1990 |
| Johnson County (this page) | 118 | 58.5% | 39% | 2.5% | 1979 |
| Schuyler County | 114 | 21.1% | 68.4% | 10.5% | 1981 |
| Jersey County | 113 | 57.5% | 38.1% | 4.4% | 1981 |
| Boone County | 109 | 56% | 37.6% | 6.4% | 1986 |
| Pulaski County | 108 | 35.2% | 56.5% | 8.3% | 1981 |
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 Johnson 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 Johnson County, both outside Illinois so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside IL (118 bridges here).
- Autauga County, AL · 118 bridges
- Perry County, AR · 118 bridges
- Montrose County, CO · 118 bridges
- Rabun County, GA · 118 bridges
Similar average build year
Nearest mean year-built outside IL (1979 here).
- Pima County, AZ · avg 1979 · 1,150 bridges
- Jefferson County, KY · avg 1979 · 662 bridges
- Spartanburg County, SC · avg 1979 · 638 bridges
- McPherson County, KS · avg 1979 · 586 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Poor-condition bridges (3)
SBI 146
PoorOver: DUTCHMAN CREEK
1.5 MI E OF ILL 37, Johnson, IL
Built 1930 Load: 13.6 t ADT: 200
FR 870
PoorOver: WAGON CREEK
.5 MILES WEST OF CR#18, Johnson, IL
Built 1967 Load: 13.9 t ADT: 29
TR 111
PoorOver: DUTCHMAN CR. TRIB.
SW1/4 SEC13 T12S R2E, Johnson, IL
Built 1978 Load: 38.2 t ADT: 225
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.