County profile · official public datasets

Boone County, IL

109 public highway bridges tracked in the FHWA National Bridge Inventory: 56% rated Good, 37.6% Fair, 6.4% Poor.

109
Public bridges
56%
Good condition
6.4%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Boone County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 33%
lowest Poor share in state
6.4%
Poor-condition share
109
public highway bridges
1986
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.

Boone County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Boone County ranks #34 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.4%). Boone County, Illinois contains 109 public highway bridges. Roughly 56% are rated “Good,” 37.6% “Fair,” and 6.4% “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

109

Public highway bridges in Boone County

Good condition

56%

61 of 109 rated 7-9

Fair condition

37.6%

41 of 109 rated 5-6

Poor condition

6.4%

7 of 109 rated 4 or below

In-state Poor-share rank

#34 of 102

Among Illinois counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 109 NBI-tracked bridges by lowest applicable component rating.

Good
56% (61)
Fair
37.6% (41)
Poor
6.4% (7)

Boone County's Poor-condition bridges carry 16,325 vehicle crossings a day

That is 3.6% of the county's reported daily bridge traffic on 6.5% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,332 crossings a day against 4,325 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 108 of 109 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

36.7% of Boone County's bridges have passed the 50-year mark

40 of the 109 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 56% 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 71.7% of the county's Poor-condition bridge traffic

S. APPLETON ROAD over KISHWAUKEE RIVER, built 1964, carries 11,700 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 7-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 16,325 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

When Boone County's bridges were built

109 bridges with a recorded construction year, grouped by decade

bridges

What this shows Construction peaked in the 2010s, when 22 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 5 to 14 years old in the 2024 inventory. Its average build year is 1986, 7 years newer than the Illinois average of 1979.

Source FHWA National Bridge Inventory (year built) As of 2024 NBI release

How Boone County compares with Illinois's closest counties by inventory size

The 5 Illinois counties nearest Boone County in number of bridges, with their condition splits. Its 6.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1986 against a peer-group mean of 1981 is 5 years newer.

Showing the 5 closest of 101 Illinois counties eligible for comparison.

Bridge inventory size and condition shares for Boone County and the 5 Illinois counties closest to it in inventory size
County Bridges Poor
Johnson County 118 2.5%
Schuyler County 114 10.5%
Jersey County 113 4.4%
Boone County (this page) 109 6.4%
Pulaski County 108 8.3%
Scott County 99 7.1%

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 Boone 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 Boone County, both outside Illinois so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IL (109 bridges here).

Similar average build year

Nearest mean year-built outside IL (1986 here).

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 109 Good 61 Fair 41 Poor 7

All bridges (109)

ROCKTON RD

Good

Over: N KINNIKINNICK CREEK

6.5 MI NE ROSCOE, Boone, IL

Built 1973 Load: 32.4 t ADT: 250

CRAWFORD ROAD

Good

Over: SPRING CREEK

6.0 MI SE BELVIDERE, Boone, IL

Built 1977 Load: 32.4 t ADT: 250

BELOIT RD

Good

Over: BEAVER CREEK

3.5 MI NW BELVIDERE, Boone, IL

Built 1978 Load: 32.4 t ADT: 3,800

FRUIT FARM ROAD

Good

Over: MOSQUITO CREEK

3.5 MI SE BELVIDERE, Boone, IL

Built 1982 Load: 32.4 t ADT: 25

CARLSON RD

Good

Over: SPRING CREEK

3.0 MI S GARDEN PRAI, Boone, IL

Built 1984 Load: 32.4 t ADT: 325

REEDS CROSSING ROA

Good

Over: MOSQUITO CREEK

4.0 MI SE BELVIDERE, Boone, IL

Built 1983 Load: 32.4 t ADT: 200

GRANGE HALL RD

Good

Over: E BR PISCASAW CR

2.5 M SE POPLAR GROV, Boone, IL

Built 1986 Load: 32.4 t ADT: 50

BLOODS POINT ROAD

Good

Over: CN RR

1.5 MI E WINN CO LN, Boone, IL

Built 1991 Load: 32.4 t ADT: 550

CALEDONIA RD

Good

Over: BEAVER CREEK

2.5 M N. OF BELVIDER, Boone, IL

Built 2003 Load: 32.4 t ADT: 3,350

MARENGO RD (TR 77)

Good

Over: MUD CREEK

1.5 MI N GARDN PRARI, Boone, IL

Built 1994 Load: 32.4 t ADT: 2,000

LAWRENCEVILLE RD

Good

Over: MUD CREEK

1.5MI. NW GARDEN PR., Boone, IL

Built 2000 Load: 32.4 t ADT: 1,400

COUNTY LINE RD

Good

Over: BR PISCASAW CREEK

1.5 MI E OF CAPRON, Boone, IL

Built 2004 Load: 32.4 t ADT: 600

GARDEN PRAIRIE RD

Good

Over: COON CREEK

1.5 MI S GARDEN PR, Boone, IL

Built 2005 Load: 32.4 t ADT: 475

IRENE RD

Good

Over: UNNAMED CREEK

1.5MI S OF US 20, Boone, IL

Built 2007 Load: 32.4 t ADT: 1,650

RIVERSIDE ROAD

Good

Over: BR OF BEAVER CR

3.5MI NE OF BELVIDER, Boone, IL

Built 2007 Load: 32.4 t ADT: 2,350

COUNTY LINE RD

Good

Over: SPRING CREEK

2 MI SE GARDEN PRAIR, Boone, IL

Built 2016 Load: 32.4 t ADT: 100

CENTERVILLE RD

Good

Over: BEAVER CREEK

2 MI W OF CAPRON, Boone, IL

Built 2013 Load: 32.4 t ADT: 150

GARDEN PRAIRIE

Good

Over: KISHWAUKEE RIVER

.5 MI N US 20, Boone, IL

Built 2015 Load: 32.4 t ADT: 2,850

POPLAR GROVE RD

Good

Over: KISHWAUKEE RIVER

NE EDGE OF BELVIDERE, Boone, IL

Built 2020 Load: 32.4 t ADT: 2,200

LIVINGSTON SCHOOL

Good

Over: SOUTH KINNIKINNICK C

3.0 MI N CALEDONIA, Boone, IL

Built 2021 Load: 32.4 t ADT: 50

TOWNLINE RD

Good

Over: BR N KINNINNICK CR

NW CORNER BOONE CO., Boone, IL

Built 1960 Load: 32.4 t ADT: 100

CALEDONIA ROAD

Good

Over: S. KINNIKINNICK CR.

3.3 MI. N. CALEDONIA, Boone, IL

Built 1995 Load: 32.4 t ADT: 1,000

POPLAR GROVE RD

Good

Over: BR. OF BEAVER CREEK

1.75 MI. N. OF IL173, Boone, IL

Built 1998 Load: 32.4 t ADT: 1,350

PEARL STREET RD

Good

Over: KINGSBURY CREEK

AT DEKALB CO. LINE, Boone, IL

Built 1999 Load: 32.4 t ADT: 500

IRENE RD

Good

Over: UNNAMED CRK

0.25 MI S OF US 20, Boone, IL

Built 1900 Load: 32.4 t ADT: 3,200

ORTH ROAD

Good

Over: BR OF BEAVER CREEK

0.6 MI. W. OF IL 76, Boone, IL

Built 2009 Load: 32.4 t ADT: 1,650

ORTH RD

Good

Over: BEAVER CREEK

4.0 MI N BELVIDERE, Boone, IL

Built 2014 Load: 32.4 t ADT: 1,650

TOWN HALL ROAD

Good

Over: UNNAMED STREAM

0.25MI S OF US 20, Boone, IL

Built 2010 Load: 32.4 t ADT: 4,950

FAS-39 (HUNTER RD)

Good

Over: BEAVER CREEK

3.0 MI NW OF CAPRON, Boone, IL

Built 2011 Load: 34.0 t ADT: 1,550

IL 173

Good

Over: BR. BEAVER CREEK

2.7 MI. E. OF IL 76, Boone, IL

Built 2000 Load: 35.0 t ADT: 4,100

PEARL ST

Good

Over: I 90

4 MI E OF US 20, Boone, IL

Built 2014 Load: 35.6 t ADT: 750

TRIPP RD

Good

Over: I-90

.5 MI S OF US 20, Boone, IL

Built 2016 Load: 37.3 t ADT: 300

COUNTY LINE RD

Good

Over: I 90

MC HENRY CO LINE, Boone, IL

Built 2014 Load: 38.6 t ADT: 250

SPRING CENTER RD

Good

Over: I 90

3 MI W MCHENRY CO, Boone, IL

Built 2016 Load: 39.5 t ADT: 75

IRENE RD

Good

Over: I 90

.5 MI S US 20, Boone, IL

Built 2013 Load: 40.5 t ADT: 1,650

IL 173

Good

Over: WILLOW CREEK

0.3 MI E WINN. CO LN, Boone, IL

Built 1994 Load: 42.1 t ADT: 6,250

SHATTUCK RD

Good

Over: I 90

2.5 MI W MCHENRY CO, Boone, IL

Built 2014 Load: 42.1 t ADT: 350

GENOA RD- FAS 37

Good

Over: I 90

.6 MI S OF US 20, Boone, IL

Built 2014 Load: 42.4 t

DENNY RD

Good

Over: GERYLINE CR

3.5 MI SE POPLAR GROVE, Boone, IL

Built 2021 Load: 42.8 t ADT: 300

JOHNSON RD

Good

Over: I 90

.5 MI S CHRYSLER DR, Boone, IL

Built 2014 Load: 43.1 t ADT: 150

IL 173

Good

Over: PISCASAW CREEKTRIB.

AT MCHENRY CO. LN., Boone, IL

Built 2001 Load: 45.4 t ADT: 5,000

I 90 WB

Good

Over: MOSQUITO CRK

3 MI SE OF BELVIDERE, Boone, IL

Built 2013 Load: 46.7 t ADT: 27,150

I 90 EB

Good

Over: MOSQUITO CKR

3 MI SE OF BELVIDERE, Boone, IL

Built 2013 Load: 48.9 t ADT: 27,150

BLAINE RD

Good

Over: BEAVER CREEK

3.0 MI NW CAPRON, Boone, IL

Built 2018 Load: 49.6 t ADT: 50

I-90

Good

Over: STREAM

3.8 MI E WINN CO LN, Boone, IL

Built 1958 Load: 50.5 t ADT: 24,800

POPLAR GROVE CREEK

Good

Over: BEAVER CREEK

1.0 MI S POPLAR GR, Boone, IL

Built 2023 Load: 58.3 t ADT: 2,550

I-90

Good

Over: STREAM

0.7 MI W MCHENRY CO, Boone, IL

Built 1958 Load: 67.4 t ADT: 27,150

IL RTE 173

Good

Over: CREEK

.23MI E OF IL 76, Boone, IL

Built 2015 Load: 73.2 t ADT: 4,850

I 90

Good

Over: STREAM

0.6 MI E STONE QUARY, Boone, IL

Built 2014 Load: 81.0 t ADT: 49,600

COUNTY LINE RD

Good

Over: BR PISCASAW CREEK

1.5 E CAPRON, Boone, IL

Built 1968 Load: 88.8 t ADT: 225

Read our methodology - how this data is sourced, computed, and verified.

Related

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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.