County profile · official public datasets

Sangamon County, IL

466 public highway bridges tracked in the FHWA National Bridge Inventory: 56.9% rated Good, 36.9% Fair, 6.2% Poor.

466
Public bridges: 56.9%
Good condition: 6.2%
Poor condition

The verdict

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

Sangamon County posts a better-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

Top 28%
lowest Poor share in state: 6.2%
Poor-condition share: 466
public highway bridges: 1981
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.

Sangamon County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Sangamon County ranks #29 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.2%). Sangamon County, Illinois contains 466 public highway bridges. Roughly 56.9% are rated “Good,” 36.9% “Fair,” and 6.2% “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

466

Public highway bridges in Sangamon County

Good condition

56.9%

265 of 466 rated 7-9

Fair condition

36.9%

172 of 466 rated 5-6

Poor condition

6.2%

29 of 466 rated 4 or below

In-state Poor-share rank

#29 of 102

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

Condition distribution

Share of 466 NBI-tracked bridges by lowest applicable component rating.

Good

56.9% (265)

Fair

36.9% (172)

Poor

6.2% (29)

Sangamon County's Poor-condition bridges carry 110,125 vehicle crossings a day

That is 5.7% of the county's reported daily bridge traffic on 6.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 3,797 crossings a day against 2,850 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 466 of 466 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

40.3% of Sangamon County's bridges have passed the 50-year mark

188 of the 466 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 56.9% 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 16.2% of the county's Poor-condition bridge traffic

I-55 (SB) over ILLINOIS CENTRAL RR, built 1971, carries 17,850 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 29-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 110,125 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

6
1910s

1
1920s

3
1930s

7
1940s

7
1950s

25
1960s

84
1970s

97
1980s

71
1990s

65
2000s

63
2010s

30
2020s

7

What this shows Construction peaked in the 1970s, when 97 of the county's bridges still in the inventory were built, which is 20.8% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1981) matches the Illinois average (1979).

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

The 5 Illinois counties nearest Sangamon County in number of bridges, with their condition splits. Its 6.2% Poor share is the 1st-lowest of these 6. Its average build year of 1981 against a peer-group mean of 1978 is in line with the group.

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

Bridge inventory size and condition shares for Sangamon County and the 5 Illinois counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
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
St. Clair County	486	50%	40.9%	9.1%	1977
Winnebago County	467	31.3%	61.7%	7.1%	1978
Sangamon County (this page)	466	56.9%	36.9%	6.2%	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 Sangamon 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 Sangamon County, both outside Illinois so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IL (466 bridges here).

Brown County, WI · 466 bridges
Broome County, NY · 468 bridges
Jefferson County, CO · 464 bridges
Hamilton County, TN · 464 bridges

Similar average build year

Nearest mean year-built outside IL (1981 here).

Franklin County, OH · avg 1981 · 922 bridges
Greenville County, SC · avg 1981 · 635 bridges
Montgomery County, OH · avg 1981 · 632 bridges
Shawnee County, KS · avg 1981 · 563 bridges

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

All 466 Good 265 Fair 172 Poor 29

All bridges (466)

Sort:

Sangamon County Bridge Snapshot

Condition distribution

Sangamon County's Poor-condition bridges carry 110,125 vehicle crossings a day

40.3% of Sangamon County's bridges have passed the 50-year mark

One structure carries 16.2% of the county's Poor-condition bridge traffic

How Sangamon 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 (466)

TR 189

TR 189

FAS 613

CH 8/FAS 613

CH 10 FAS 621

COUNTY HWY 21

RT621 14.WCOUNTY 1

FAS 622/CH 15

CH-15

FAS623-CH45

CH 45 FAS623

FAS624-CH40

FAU 7998

FAU 7998 CH 40

FAS 624A (CH 40)

FAS 624A (CH 40)

CH 47

COUNTY HWY 12

COUNTY HWY 6

COUNTY HWY 28

CH 29

COUNTY HWY 2

COUNTY HWY 46

CH 48

CH 56

TR 478

FAS 623 CH 45

FAS 0625

TR 7 (9.5N)

TR 7 (10N)

TR 7

TR 11 H

TR 139

TR 20

TR 33 (7.5N)

TR 34 (14W)

TR 466

TR 56(12.75AW)

TR 76 (11.25W)

TR 82

TR 104

TR 104

FAU 8149

TR 108

TR 122

TR 7.75 W

TR 130 (7.75W)

TR134 AUBURN

TR 150

TR 155

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