County profile · official public datasets

Mason County, IL

86 public highway bridges tracked in the FHWA National Bridge Inventory: 33.7% rated Good, 61.6% Fair, 4.7% Poor.

86
Public bridges: 33.7%
Good condition: 4.7%
Poor condition

The verdict

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

Mason County posts a top-quartile lowest Poor-condition share among rated counties in the state across rated county bridge inventory.

Top 12%
lowest Poor share in state: 4.7%
Poor-condition share: 86
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.

Mason County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Mason County ranks #12 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 4.7%). Mason County, Illinois contains 86 public highway bridges. Roughly 33.7% are rated “Good,” 61.6% “Fair,” and 4.7% “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

Public highway bridges in Mason County

Good condition

33.7%

29 of 86 rated 7-9

Fair condition

61.6%

53 of 86 rated 5-6

Poor condition

4.7%

4 of 86 rated 4 or below

In-state Poor-share rank

#12 of 102

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

Condition distribution

Share of 86 NBI-tracked bridges by lowest applicable component rating.

Good

33.7% (29)

Fair

61.6% (53)

Poor

4.7% (4)

Mason County's Poor-condition bridges carry 200 vehicle crossings a day

That is 0.5% of the county's reported daily bridge traffic on 4.7% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 50 crossings a day against 421 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 86 of 86 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

36% of Mason County's bridges have passed the 50-year mark

31 of the 86 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 33.7% 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 37.5% of the county's Poor-condition bridge traffic

COUNTY HIGHWAY 11 over RED OAK DITCH, built 1954, carries 75 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 4-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 200 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1910s

1
1920s

3
1930s

1
1940s

2
1950s

8
1960s

5
1970s

18
1980s

21
1990s

9
2000s

6
2010s

10
2020s

1

What this shows Construction peaked in the 1980s, when 21 of the county's bridges still in the inventory were built, which is 24.4% 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 Mason County compares with Illinois's closest counties by inventory size

The 5 Illinois counties nearest Mason County in number of bridges, with their condition splits. Its 4.7% Poor share is the 2nd-lowest of these 6. Its average build year of 1980 against a peer-group mean of 1983 is in line with the group.

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

Bridge inventory size and condition shares for Mason County and the 5 Illinois counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Menard County	89	40.4%	49.4%	10.1%	1980
Wabash County	89	61.8%	32.6%	5.6%	1983
Pope County	88	63.6%	29.5%	6.8%	1983
Mason County (this page)	86	33.7%	61.6%	4.7%	1980
Gallatin County	82	78%	13.4%	8.5%	1984
Calhoun County	81	53.1%	43.2%	3.7%	1983

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

Similar inventory size

Nearest county inventories outside IL (86 bridges here).

Catoosa County, GA · 86 bridges
Starke County, IN · 86 bridges
Columbia County, WA · 86 bridges
Modoc County, CA · 87 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 86 Good 29 Fair 53 Poor 4

All bridges (86)

Sort:

US 136

Fair

Over: RED OAK DITCH

3.5 MI W JCT 29&136, Mason, IL

Built 1962 Load: 40.2 t ADT: 1,150

TR 105

Fair

Over: WHITE OAK CREEK

2.5 MI S HAVANA, Mason, IL

Built 1964 Load: 45.0 t ADT: 25

IL 29

Fair

Over: SLEEPY HOLLOW DITCH

1.5M N MENARD COUNTY, Mason, IL

Mason County Bridge Snapshot

Condition distribution

Mason County's Poor-condition bridges carry 200 vehicle crossings a day

36% of Mason County's bridges have passed the 50-year mark

One structure carries 37.5% of the county's Poor-condition bridge traffic

How Mason 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 (86)

US 136

TR 105

IL 29

ILL 97

ILL 29

TR 41

FAS 568 CH3

FAS 1585(CH 21)

FAS 572 CH 5

FAS 1595 (CH 19)

FAS 1587 / CH 2

FAS 1587 / CH 2

FAS 1587

COUNTY HIGHWAY 4

COUNTY HIGHWAY 4

COUNTY HIGHWAY 4

TR 39

TR 47

TR 59

TR 59

TR 266

TR 75

TR 10

TR 129

TR 171

TR 178

FAS 1586

TR 234

ILL 10

ILL 10

TR 125

FAS 567 (CH 20)

TR 208

COUNTY HIGHWAY 11

TR 153

TR 190

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