County profile · official public datasets

Stillwater County, MT

92 public highway bridges tracked in the FHWA National Bridge Inventory: 30.4% rated Good, 68.5% Fair, 1.1% Poor.

92
Public bridges: 30.4%
Good condition: 1.1%
Poor condition

The verdict

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

Stillwater County posts a top-10% lowest Poor-condition share among rated counties in the state across rated county bridge inventory.

Top 7%
lowest Poor share in state: 1.1%
Poor-condition share: 92
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.

Stillwater County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Stillwater County ranks #4 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 1.1%). Stillwater County, Montana contains 92 public highway bridges. Roughly 30.4% are rated “Good,” 68.5% “Fair,” and 1.1% “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 Stillwater County

Good condition

30.4%

28 of 92 rated 7-9

Fair condition

68.5%

63 of 92 rated 5-6

Poor condition

1.1%

1 of 92 rated 4 or below

In-state Poor-share rank

#4 of 56

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

Condition distribution

Share of 92 NBI-tracked bridges by lowest applicable component rating.

Good

30.4% (28)

Fair

68.5% (63)

Poor

1.1% (1)

Stillwater County's Poor-condition bridges carry 4,987 vehicle crossings a day

That is 1.9% of the county's reported daily bridge traffic on 1.1% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 4,987 crossings a day against 1,660 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 92 of 92 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

58.7% of Stillwater County's bridges have passed the 50-year mark

54 of the 92 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 30.4% 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 100% of the county's Poor-condition bridge traffic

S 78 over YELLOWSTONE RIVER, built 1957, carries 4,987 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 1-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 4,987 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

7
1930s

4
1940s

2
1950s

2
1960s

13
1970s

29
1980s

2
1990s

7
2000s

18
2010s

7
2020s

1

What this shows Construction peaked in the 1970s, when 29 of the county's bridges still in the inventory were built, which is 31.5% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1977) matches the Montana average (1977).

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

The 5 Montana counties nearest Stillwater County in number of bridges, with their condition splits. Its 1.1% Poor share is the 1st-lowest of these 6. Its average build year of 1977 against a peer-group mean of 1979 is in line with the group.

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

Bridge inventory size and condition shares for Stillwater County and the 5 Montana counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Phillips County	101	13.9%	69.3%	16.8%	1972
Madison County	97	32%	56.7%	11.3%	1981
Richland County	97	28.9%	68%	3.1%	1988
Pondera County	96	51%	44.8%	4.2%	1975
Sweet Grass County	94	28.7%	66%	5.3%	1977
Stillwater County (this page)	92	30.4%	68.5%	1.1%	1977

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

Similar inventory size

Nearest county inventories outside MT (92 bridges here).

Douglas County, GA · 92 bridges
Taylor County, KY · 92 bridges
Waldo County, ME · 92 bridges
Camden County, MO · 92 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 92 Good 28 Fair 63 Poor 1

Fair-condition bridges (63)

Sort:

Stillwater County Bridge Snapshot

Condition distribution

Stillwater County's Poor-condition bridges carry 4,987 vehicle crossings a day

58.7% of Stillwater County's bridges have passed the 50-year mark

One structure carries 100% of the county's Poor-condition bridge traffic

How Stillwater 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

Fair-condition bridges (63)

I 90

I 90

OLD US 10

WOODBINE CAMPGRD

1-LANE ROAD

CEMETERY RD

OLD US 10

I 90

FRONTAGE ROAD 120

OLD US 10

NITCHE RD

I 90

RAPELJE RD

I 90

OLD US 10

OLD US 10

I 90

I 90

I 90

REED POINT RD

OLD US 10

OLD US 10

OLD US 10

I 90

I 90

NYE RD-S 419

VALLEY CREEK RD

I 90

I 90

I 90

I 90

1ST ST NW

I 90

I 90

I 90

RAPELJE RD

I 90

WHITEBIRD CR RD

I 90

OLD US 10

I 90

I 90

COLUMBUS-MOLT RD

I 90

OLD US 10

S 78

COUNTRYMAN CR RD

YOUNGS POINT RD

S 78

NYE RD-S 419

Related