County profile · official public datasets

St. Clair County, MO

139 public highway bridges tracked in the FHWA National Bridge Inventory: 25.2% rated Good, 55.4% Fair, 19.4% Poor.

139
Public bridges: 25.2%
Good condition: 19.4%
Poor condition

The verdict

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

St. Clair County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.

108th
of 115 on Poor share: 19.4%
Poor-condition share: 139
public highway bridges: 1972
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.

St. Clair County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, St. Clair County ranks #108 of 115 Missouri counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 19.4%). St. Clair County, Missouri contains 139 public highway bridges. Roughly 25.2% are rated “Good,” 55.4% “Fair,” and 19.4% “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

139

Public highway bridges in St. Clair County

Good condition

25.2%

35 of 139 rated 7-9

Fair condition

55.4%

77 of 139 rated 5-6

Poor condition

19.4%

27 of 139 rated 4 or below

In-state Poor-share rank

#108 of 115

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

Condition distribution

Share of 139 NBI-tracked bridges by lowest applicable component rating.

Good

25.2% (35)

Fair

55.4% (77)

Poor

19.4% (27)

St. Clair County's Poor-condition bridges carry 19,643 vehicle crossings a day

That is 11.6% of the county's reported daily bridge traffic on 19.4% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 728 crossings a day against 2,062 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 139 of 139 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

45.3% of St. Clair County's bridges have passed the 50-year mark

63 of the 139 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 25.2% 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 48% of the county's Poor-condition bridge traffic

MO 13 N over OTTER CR, built 1963, carries 9,437 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 27-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 19,643 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1910s

3
1920s

4
1930s

21
1940s

9
1950s

10
1960s

13
1970s

21
1980s

8
1990s

9
2000s

27
2010s

10
2020s

3

What this shows Construction peaked in the 2000s, when 27 of the county's bridges still in the inventory were built, which is 19.4% of those with a recorded year. That cohort is now 15 to 24 years old in the 2024 inventory. Its average build year is 1972, 7 years older than the Missouri average of 1979.

How St. Clair County compares with Missouri's closest counties by inventory size

The 5 Missouri counties nearest St. Clair County in number of bridges, with their condition splits. Its 19.4% Poor share is the 5th-lowest of these 6. Its average build year of 1972 against a peer-group mean of 1972 is in line with the group.

Showing the 5 closest of 114 Missouri counties eligible for comparison.

Bridge inventory size and condition shares for St. Clair County and the 5 Missouri counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Gasconade County	143	32.2%	62.9%	4.9%	1972
Miller County	142	40.1%	49.3%	10.6%	1971
St. Clair County (this page)	139	25.2%	55.4%	19.4%	1972
Ralls County	138	31.9%	60.9%	7.2%	1976
Mercer County	137	44.5%	36.5%	19%	1976
Benton County	135	11.9%	67.4%	20.7%	1964

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 St. Clair 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 St. Clair County, both outside Missouri so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MO (139 bridges here).

Bulloch County, GA · 139 bridges
St. Helena County, LA · 139 bridges
Garrett County, MD · 139 bridges
Midland County, MI · 139 bridges

Similar average build year

Nearest mean year-built outside MO (1972 here).

Santa Clara County, CA · avg 1972 · 964 bridges
Madison County, AL · avg 1972 · 710 bridges
Kern County, CA · avg 1972 · 668 bridges
York County, PA · avg 1972 · 569 bridges

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

All 139 Good 35 Fair 77 Poor 27

All bridges (139)

Sort:

St. Clair County Bridge Snapshot

Condition distribution

St. Clair County's Poor-condition bridges carry 19,643 vehicle crossings a day

45.3% of St. Clair County's bridges have passed the 50-year mark

One structure carries 48% of the county's Poor-condition bridge traffic

How St. Clair County compares with Missouri'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 (139)

COUNTY RD NW 1401

COUNTY RD NW 451

COUNTY RD NW 1000

COUNTY RD SE 1425

COUNTY RD SE 50

COUNTY RD SW 600

COUNTY RD NW 1270

COUNTY RD NW 1000

COUNTY RD NW 501

COUNTY RD NE 175

NE OLD 13 HWY

COUNTY RD SW 50

FIRST ST

COUNTY RD NW 630

RT V S

COUNTY RD NW 1150

COUNTY RD SE 601

RT T E

RT B E

COUNTY RD SE 801

RT O E

COUNTY RD SE 451

RT H S

RT B E

RT BB E

RT D S

COUNTY RD SE 450

COUNTY RD NE 1301

RT H S

MO 82 E

RT TT E

RT P S

COUNTY RD NW 776

COUNTY RD NW 726

COUNTY RD NW 176

COUNTY RD SW 366

RT C E

RT M S

COUNTY RD NW 100

MO 82 E

RT B E

COUNTY RD NW 400

MO 82 E

RT V S

MO 13 S

COUNTY RD SW 401

COUNTY RD NW 1101

US 54 E

COUNTY RD SW 1371

COUNTY RD SW 1371

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