County profile · official public datasets

Hamilton County, IA

165 public highway bridges tracked in the FHWA National Bridge Inventory: 39.4% rated Good, 40% Fair, 20.6% Poor.

165
Public bridges: 39.4%
Good condition: 20.6%
Poor condition

The verdict

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

Hamilton 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.

57th
of 99 on Poor share: 20.6%
Poor-condition share: 165
public highway bridges: 1970
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.

Hamilton County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Hamilton County ranks #57 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 20.6%). Hamilton County, Iowa contains 165 public highway bridges. Roughly 39.4% are rated “Good,” 40% “Fair,” and 20.6% “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

165

Public highway bridges in Hamilton County

Good condition

39.4%

65 of 165 rated 7-9

Fair condition

40%

66 of 165 rated 5-6

Poor condition

20.6%

34 of 165 rated 4 or below

In-state Poor-share rank

#57 of 99

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

Condition distribution

Share of 165 NBI-tracked bridges by lowest applicable component rating.

Good

39.4% (65)

Fair

40% (66)

Poor

20.6% (34)

Hamilton County's Poor-condition bridges carry 4,871 vehicle crossings a day

That is 1.5% of the county's reported daily bridge traffic on 20.1% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 148 crossings a day against 1,889 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 164 of 165 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

57.6% of Hamilton County's bridges have passed the 50-year mark

95 of the 165 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 39.4% 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 14.3% of the county's Poor-condition bridge traffic

FM over SKUNK RIVER, built 1974, carries 698 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 34-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 4,871 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

2
1910s

6
1920s

18
1930s

4
1940s

5
1950s

16
1960s

23
1970s

41
1980s

6
1990s

14
2000s

14
2010s

14
2020s

2

What this shows Construction peaked in the 1970s, when 41 of the county's bridges still in the inventory were built, which is 24.8% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year is 1970, 9 years older than the Iowa average of 1979.

How Hamilton County compares with Iowa's closest counties by inventory size

The 5 Iowa counties nearest Hamilton County in number of bridges, with their condition splits. Its 20.6% Poor share is the 4th-lowest of these 6. Its average build year of 1970 against a peer-group mean of 1981 is 11 years older.

Showing the 5 closest of 98 Iowa counties eligible for comparison.

Bridge inventory size and condition shares for Hamilton County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Clarke County	168	27.4%	41.1%	31.5%	1977
Greene County	168	35.1%	50%	14.9%	1973
Mitchell County	167	47.3%	42.5%	10.2%	1980
Davis County	165	44.8%	29.7%	25.5%	1985
Hamilton County (this page)	165	39.4%	40%	20.6%	1970
Wayne County	163	44.2%	37.4%	18.4%	1989

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

Similar inventory size

Nearest county inventories outside IA (165 bridges here).

Cleburne County, AL · 165 bridges
Randolph County, AL · 165 bridges
Plumas County, CA · 165 bridges
Leon County, FL · 165 bridges

Similar average build year

Nearest mean year-built outside IA (1970 here).

Hamilton County, OH · avg 1970 · 783 bridges
Yavapai County, AZ · avg 1970 · 543 bridges
Garfield County, OK · avg 1970 · 504 bridges
San Luis Obispo County, CA · avg 1970 · 401 bridges

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

All 165 Good 65 Fair 66 Poor 34

Fair-condition bridges (66)

Sort:

Hamilton County Bridge Snapshot

Condition distribution

Hamilton County's Poor-condition bridges carry 4,871 vehicle crossings a day

57.6% of Hamilton County's bridges have passed the 50-year mark

One structure carries 14.3% of the county's Poor-condition bridge traffic

How Hamilton County compares with Iowa'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 (66)

LOCAL

LOCAL

DES MOINES ST

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

FM

LOCAL

LOCAL

LOCAL

IA 17

IA 175

DUBUQUE ST

US 20 & IA 17

SR 350TH STREET

SR D-47

EB US 20

WB US 20

FM

WB US 20

I 35

FM

EB US 20

LOCAL

2ND ST

I 35 SB

FM

LOCAL

IA 17

WILLSON AVE

I 35 NB

IA 175

I 35 SB

2ND ST

SR D-65

LOCAL

SUPERIOR ST

KANTOR AVE

FM

LOCAL

LOCAL

LOCAL

LOCAL

IA 175

WB US 20

FM

EB US 20

FM

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