County profile · official public datasets

Mercer County, IL

163 public highway bridges tracked in the FHWA National Bridge Inventory: 50.9% rated Good, 42.3% Fair, 6.7% Poor.

163
Public bridges: 50.9%
Good condition: 6.7%
Poor condition

The verdict

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

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

Top 39%
lowest Poor share in state: 6.7%
Poor-condition share: 163
public highway bridges: 1982
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.

Mercer County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Mercer County ranks #40 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.7%). Mercer County, Illinois contains 163 public highway bridges. Roughly 50.9% are rated “Good,” 42.3% “Fair,” and 6.7% “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

163

Public highway bridges in Mercer County

Good condition

50.9%

83 of 163 rated 7-9

Fair condition

42.3%

69 of 163 rated 5-6

Poor condition

6.7%

11 of 163 rated 4 or below

In-state Poor-share rank

#40 of 102

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

Condition distribution

Share of 163 NBI-tracked bridges by lowest applicable component rating.

Good

50.9% (83)

Fair

42.3% (69)

Poor

6.7% (11)

Mercer County's Poor-condition bridges carry 5,800 vehicle crossings a day

That is 11.4% of the county's reported daily bridge traffic on 6.7% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 527 crossings a day against 104 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 163 of 163 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

26.4% of Mercer County's bridges have passed the 50-year mark

43 of the 163 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 50.9% 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 44.8% of the county's Poor-condition bridge traffic

US 67 over POPE CR, built 1931, carries 2,600 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 11-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 5,800 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

4
1920s

2
1930s

2
1940s

3
1950s

7
1960s

15
1970s

24
1980s

48
1990s

33
2000s

13
2010s

8
2020s

4

What this shows Construction peaked in the 1980s, when 48 of the county's bridges still in the inventory were built, which is 29.4% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year (1982) matches the Illinois average (1979).

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

The 5 Illinois counties nearest Mercer County in number of bridges, with their condition splits. Its 6.7% Poor share is the 4th-lowest of these 6. Its average build year of 1982 against a peer-group mean of 1980 is in line with the group.

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

Bridge inventory size and condition shares for Mercer County and the 5 Illinois counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Cumberland County	169	54.4%	39.1%	6.5%	1979
Clay County	166	49.4%	37.3%	13.3%	1982
Hamilton County	165	80%	17.6%	2.4%	1989
Mercer County (this page)	163	50.9%	42.3%	6.7%	1982
Bond County	162	45.7%	46.3%	8%	1971
Greene County	162	51.9%	42.6%	5.6%	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 Mercer 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 Mercer County, both outside Illinois so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IL (163 bridges here).

Jennings County, IN · 163 bridges
Wayne County, IA · 163 bridges
Jackson County, LA · 163 bridges
Lapeer County, MI · 163 bridges

Similar average build year

Nearest mean year-built outside IL (1982 here).

Oklahoma County, OK · avg 1982 · 1,216 bridges
Jackson County, MO · avg 1982 · 930 bridges
Milwaukee County, WI · avg 1982 · 893 bridges
Broward County, FL · avg 1982 · 686 bridges

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

All 163 Good 83 Fair 69 Poor 11

All bridges (163)

Sort:

Mercer County Bridge Snapshot

Condition distribution

Mercer County's Poor-condition bridges carry 5,800 vehicle crossings a day

26.4% of Mercer County's bridges have passed the 50-year mark

One structure carries 44.8% of the county's Poor-condition bridge traffic

How Mercer 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 (163)

TR 100

TR 42

TR 284

TR 268

TR 107

TR 240

TR 260

TR 252

TR 266

TR 274

TR 183A

TR 198A

TR 230

TR 136B

TR 158

TR 132

TR 193A

TR 100A

TR 52

TR 109

TR 111

TR 2

TR 262

TR 97

TR 208

TR 176

TR 40

TR 58

TR 59

TR 40

TR 3

TR 8

TR 228

FAS 214

TR 95

TR 206

TR 264

TR 205

TR 290B

TR 69

TR 59

TR 97

TR 164

FAS 212 (CH 9)

TR 133

TR 206

TR 244

TR 45

TR 124

TR 192

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