The Minnesota Administrative Rules, section 1300.0120, Subp. 4. A (4) states the only retaining walls except from a permit are:

retaining walls that are not over four feet (1,219 mm) in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge or impounding Class I, II, or III-A liquids;

In addition, the 2020 Minnesota Residential Code states:

R404.4 Retaining walls.

Retaining walls that are not laterally supported at the top and that retain in excess of 48 inches (1219 mm) of unbalanced fill, or retaining walls exceeding 24 inches (610 mm) in height that resist lateral loads in addition to soil, shall be designed in accordance with accepted engineering practice to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning. This section shall not apply to foundation walls supporting buildings.

Any wall over 4-ft or any wall over 2-ft supporting a surcharge requires engineering. DIY Retaining Wall provides engineering services in Minnesota.

The frost depth is 5-ft in Zone I and 3.5-ft in Zone II based on what county you are in. Concrete walls with a poured concrete footing must extend to the frost depth, while SRW walls do not need embedment that exceeds the frost depth due to their flexibility.

The City of Saint Paul and Ramsey County generally only allow segmental retaining walls and CMU or poured concrete walls without special permission.

Eagan requires a Zoning Permit for walls less than 4-ft. A building permit is still required per the requirements listed above.