County profile · official public datasets

Jefferson County, MT

134 public highway bridges tracked in the FHWA National Bridge Inventory: 17.9% rated Good, 76.9% Fair, 5.2% Poor.

134
Public bridges: 17.9%
Good condition: 5.2%
Poor condition

The verdict

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

Jefferson 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: 5.2%
Poor-condition share: 134
public highway bridges: 1977
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.

Jefferson County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Jefferson County ranks #22 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.2%). Jefferson County, Montana contains 134 public highway bridges. Roughly 17.9% are rated “Good,” 76.9% “Fair,” and 5.2% “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

134

Public highway bridges in Jefferson County

Good condition

17.9%

24 of 134 rated 7-9

Fair condition

76.9%

103 of 134 rated 5-6

Poor condition

5.2%

7 of 134 rated 4 or below

In-state Poor-share rank

#22 of 56

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

Condition distribution

Share of 134 NBI-tracked bridges by lowest applicable component rating.

Good

17.9% (24)

Fair

76.9% (103)

Poor

5.2% (7)

Jefferson County's Poor-condition bridges carry 3,221 vehicle crossings a day

That is 1.4% of the county's reported daily bridge traffic on 5.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 460 crossings a day against 1,602 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 134 of 134 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

45.5% of Jefferson County's bridges have passed the 50-year mark

61 of the 134 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 17.9% 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 55.9% of the county's Poor-condition bridge traffic

MT 55 over FISH CREEK, built 1953, carries 1,799 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 3,221 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1930s

9
1950s

4
1960s

39
1970s

20
1980s

41
1990s

2
2000s

9
2010s

6
2020s

3

What this shows Construction peaked in the 1980s, when 41 of the county's bridges still in the inventory were built, which is 30.6% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year (1977) matches the Montana average (1977).

How Jefferson County compares with Montana's closest counties by inventory size

The 5 Montana counties nearest Jefferson County in number of bridges, with their condition splits. Its 5.2% Poor share is the 2nd-lowest of these 6. Its average build year of 1977 against a peer-group mean of 1982 is 5 years older.

Showing the 5 closest of 55 Montana counties eligible for comparison.

Bridge inventory size and condition shares for Jefferson County and the 5 Montana counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Ravalli County	148	41.2%	53.4%	5.4%	1981
Big Horn County	135	26.7%	68.1%	5.2%	1978
Jefferson County (this page)	134	17.9%	76.9%	5.2%	1977
Park County	124	21%	68.5%	10.5%	1976
Sanders County	120	40%	52.5%	7.5%	1979
Lake County	117	57.3%	27.4%	15.4%	1995

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

Similar inventory size

Nearest county inventories outside MT (134 bridges here).

Anchorage County, AK · 134 bridges
Knott County, KY · 134 bridges
Murray County, MN · 134 bridges
Steele County, MN · 134 bridges

Similar average build year

Nearest mean year-built outside MT (1977 here).

San Diego County, CA · avg 1977 · 1,632 bridges
King County, WA · avg 1977 · 1,238 bridges
Riverside County, CA · avg 1977 · 1,117 bridges
Shelby County, TN · avg 1977 · 1,077 bridges

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

All 134 Good 24 Fair 103 Poor 7

All bridges (134)

Sort:

Jefferson County Bridge Snapshot

Condition distribution

Jefferson County's Poor-condition bridges carry 3,221 vehicle crossings a day

45.5% of Jefferson County's bridges have passed the 50-year mark

One structure carries 55.9% of the county's Poor-condition bridge traffic

How Jefferson County compares with Montana'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 (134)

NON MAINTAINED TRL

NON MAINTAINED TRL

BOULDER CUT OFF RD

LOWER VALLEY RD -

S HILLS RD-HWY 282

TEBAY LN

WHITETAIL RD

I 15

NO DATA ENTERED

I 90

I 15

S 69

I 90

BASIN ST

I 15

MT HWY 2

S 2

S 2

E 1ST STREET

GALENA GULCH ROAD

I 15

I 15

CATTLE DRIVE RD

I 15 FRONTAGE RD

MT HWY 2

TEBAY LN

S 41

I 15

I 15

I 15

I 15

I 15

I 15

BASIN CREEK RD

I 15 FRONTAGE RD

MILLIGAN CANYON RD

I 15 FRONTAGE RD

WHITE BRIDGE RD

I 15

I 15

I 15

I 15

PAUL GULCH RD

WATERLOO RD

I 15

I 15

I 15

I 15 FRONTAGE RD

SHAMROCK ROAD

I 15

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