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.

Total bridges

118

Public highway bridges in Johnson County

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.

1900s

1
1920s

3
1930s

9
1940s

1
1950s

3
1960s

3
1970s

37
1980s

24
1990s

15
2000s

13
2010s

7
2020s

2

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.

Bridge inventory size and condition shares for Johnson County and the 5 Illinois counties closest to it in inventory size
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.

All 118 Good 69 Fair 46 Poor 3

All bridges (118)

Sort:

Johnson County Bridge Snapshot

Condition distribution

Johnson County's Poor-condition bridges carry 454 vehicle crossings a day

42.4% of Johnson County's bridges have passed the 50-year mark

One structure carries 49.6% of the county's Poor-condition bridge traffic

How Johnson 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 (118)

TR 35

TR 142

TR 153

TR 13

TR 131

TR 182

TR138

TR 186

FAS 931

FAS 931

TR 131

TR 77

TR 70

TR 24

TR 15

CS 3650

TR 96

OR 7650D

TR 107

TR 153

TR 109

TR 38

TR 70

TR 233

TR 92

TR 131

FAS 940

TR 140

TR 89-ALLEN ROAD

TR 35-BELVILLE RD

TR 190

TR215 W.WHITEHILL

TR 192-WALNUT GROV

TR100-INDIANPOINT

TR 221 CROSSROADS

RAILROAD ST

Luther Chapel Road

PLEASANT GROVE RD

WELLINGTON RD-TR 2

SOUTH FORK LANE

DOUBLE BRIDGE LA

MCKINLEY LN

TREAT LANE

IL 146

TR 109

TWP RD 111

TR 225

US 45

ILL 147

CREAL SPRINGS ROAD

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