The following is a guide to usage of county road shields in Minnesota counties. There is no hard-and-fast rule, although many rural counties use the white square exclusively, while some metro counties use only the blue pentagon. Some use the pentagon for county state-aid highways and the square for others, some reserve the pentagon for a select few CSAHs.
In some cases, the blue pentagonal shield will be officially in use for some or all county roads, yet the square markers will remain in place in some spots, usually guide signs on intersecting roads. (Example: For Grant CSAH 4 in Elbow Lake, the guide sign on MN-59 is square, but the route marker on CSAH 4 is a pentagon.)
Where possible, the map or county document is cited. Much of the rest came from personal observation or checking the route makers on Google Maps' street view.
Aitkin
All county roads use the square shield.
Anoka
All county roads use the pentagonal shield.
Becker
All county roads use the square shield.
Beltrami
All county roads use the square shield.
Benton
All county roads use the square shield.
Big Stone
All county roads use the square shield.
Blue Earth
All county roads use the pentagonal shield.
Brown
County state-aid highways (1- and 2-digit) use the pentagonal shield, others (3-digit) use the square. [1]
Carlton
All county roads use the square shield.
Carver
All county roads use the square shield.
Cass
All county roads use the square shield.
Chippewa
All county roads use the square shield.
Chisago
County state-aid highway used the pentagonal shield
County state-aid highways use the pentagonal shield. Others probably use the square but not sure.
Lyon
Mahnomen
Marshall
All county roads use the square shield.
Martin
County state-aid highways use the pentagonal shield, others use the square according to [7], all use the square according to Google Maps street view.
McLeod
County state-aid highways use the pentagonal shield, others use the square shield.
Meeker
Mille Lacs
All county roads use the square shield.
Morrison
All county roads use the square shield.
Mower
All county roads use the pentagonal shield.
Murray
All county roads use the pentagonal shield.
Nicollet
All county roads use the square shield.
Nobles
County state-aid highways use the pentagonal shield, others unknown.
Norman
Olmsted
All county roads use the square shield.
Otter Tail
All county roads use the square shield.
Pennington
County state-aid highways use the pentagonal shield, others use the square.
Pine
All county roads use the square shield.
Pipestone
All county roads use the square shield.
Polk
All county roads use the square shield.
Pope
County state-aid highways use the pentagonal shield, others unknown.
Ramsey
All county roads use the pentagonal shield.
Red Lake
County state-aid highways use the pentagonal shield, others unknown.
Redwood
County state-aid highways use the pentagonal shield, others unknown.
Renville
County state-aid highways use the pentagonal shield, others use the square shield.
Rice
All county roads use the square shield except CSAH 33.
Rock
All county roads use the square shield.
Roseau
St. Louis
County state-aid highways "of special significance" use the blue shield, others use the square one. The road restriction maps denote which roads are such.
Scott
All county roads use the pentagonal shield.
Sherburne
All county roads use the square shield.
Stearns
County state-aid highways use the blue pentagonal shield, others use the square one. **Not verified**
Steele
All county roads use the square shield except where CSAH 12, 22, and 23 meet at the Medford interchange on Interstate 35.
Stevens
Swift
Todd
All county roads use the square shield.
Traverse
Wabasha
Wadena
Waseca
All county roads use the square shield.
Washington
County state-aid highways (1-38 and 59 except "A" suffix, "B" suffix, 27, and 28) use the pentagonal shield, others (39 and higher (except 59), "A" suffix, "B" suffix, 27 and 28) use the square one. 83 used pentagonal shields and square shields interchangeably when it existed. [8]
Watonwan
All county roads use the square shield.
Wilkin
Winona
All county roads use the square shield
Wright
County state-aid highways (1- and 2-digit) use the pentagonal shield, others (3-digit) use the square one. [9]
Yellow Medicine
County state-aid highways use the pentagonal shield, others unknown.