County profile · official public datasets

Rock County, MN

265 public highway bridges tracked in the FHWA National Bridge Inventory: 80% rated Good, 17.7% Fair, 2.3% Poor.

265
Public bridges: 80%
Good condition: 2.3%
Poor condition

The verdict

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

Rock County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 26%
lowest Poor share in state: 2.3%
Poor-condition share: 265
public highway bridges: 1991
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.

Rock County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Rock County ranks #23 of 87 Minnesota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 2.3%). Rock County, Minnesota contains 265 public highway bridges. Roughly 80% are rated “Good,” 17.7% “Fair,” and 2.3% “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

265

Public highway bridges in Rock County

Good condition

80%

212 of 265 rated 7-9

Fair condition

17.7%

47 of 265 rated 5-6

Poor condition

2.3%

6 of 265 rated 4 or below

In-state Poor-share rank

#23 of 87

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

Condition distribution

Share of 265 NBI-tracked bridges by lowest applicable component rating.

Good

80% (212)

Fair

17.7% (47)

Poor

2.3% (6)

Rock County's Poor-condition bridges carry 2,616 vehicle crossings a day

That is 1.3% of the county's reported daily bridge traffic on 2.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 436 crossings a day against 338 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 265 of 265 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

22.3% of Rock County's bridges have passed the 50-year mark

59 of the 265 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 80% 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 38.5% of the county's Poor-condition bridge traffic

CSAH 6 over I 90, built 1964, carries 1,006 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 6-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 2,616 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

2
1920s

6
1930s

5
1950s

8
1960s

27
1970s

16
1980s

31
1990s

62
2000s

58
2010s

43
2020s

7

What this shows Construction peaked in the 1990s, when 62 of the county's bridges still in the inventory were built, which is 23.4% of those with a recorded year. That cohort is now 25 to 34 years old in the 2024 inventory. Its average build year is 1991, 5 years newer than the Minnesota average of 1986.

How Rock County compares with Minnesota's closest counties by inventory size

The 5 Minnesota counties nearest Rock County in number of bridges, with their condition splits. Its 2.3% Poor share is the 2nd-lowest of these 6. Its average build year of 1991 against a peer-group mean of 1984 is 7 years newer.

Showing the 5 closest of 86 Minnesota counties eligible for comparison.

Bridge inventory size and condition shares for Rock County and the 5 Minnesota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Polk County	268	63.1%	33.6%	3.4%	1989
Rock County (this page)	265	80%	17.7%	2.3%	1991
Dakota County	259	44%	54.4%	1.5%	1986
Winona County	237	43%	52.3%	4.6%	1982
Lyon County	234	75.2%	21.8%	3%	1983
Stearns County	229	54.6%	42.8%	2.6%	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 Rock 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 Rock County, both outside Minnesota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MN (265 bridges here).

Chatham County, GA · 265 bridges
Henry County, OH · 265 bridges
McCurtain County, OK · 265 bridges
Lawrence County, PA · 265 bridges

Similar average build year

Nearest mean year-built outside MN (1991 here).

Denver County, CO · avg 1991 · 458 bridges
Baldwin County, AL · avg 1991 · 381 bridges
Union County, NC · avg 1991 · 353 bridges
Alcorn County, MS · avg 1991 · 213 bridges

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

All 265 Good 212 Fair 47 Poor 6

All bridges (265)

Sort:

Rock County Bridge Snapshot

Condition distribution

Rock County's Poor-condition bridges carry 2,616 vehicle crossings a day

22.3% of Rock County's bridges have passed the 50-year mark

One structure carries 38.5% of the county's Poor-condition bridge traffic

How Rock County compares with Minnesota'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 (265)

T 64

T 64

T 73

CSAH 4

CSAH 4

CSAH 4

I 90

CSAH 1

M 75

T 8

CSAH 5

CSAH 9

CSAH 1

CSAH 16

T 64

T 76

T 73

T 76

T 111

CSAH 1

CSAH 13

CSAH 13

T 8

CSAH 3

CR 59

T 146

CR 59

T 55

CSAH 12

CR 59

CR 65

CR 55

CSAH 15

M 20

CSAH 7

CSAH 6

M 43

US 75

T 45

T 32

T 32

M 18

T 100

I 90

I 90

T 23

T 142

CSAH 9

CR 58

T 70

Related