When Does Mille Lacs Freeze? Ice-In Dates by Year

Mille Lacs typically locks up in the first week of December. The Minnesota DNR State Climatology Office lists a median ice-in date of December 3 for the lake. Its earliest recorded ice-in is November 19 (1996). Its latest is December 22 (2001). The record starts in 1979 and has 17 different years of data through 2025.

In the nine most recent years the DNR lists, ice-in fell between November 26 and December 13. The most recent entry is December 4, 2025.

No ice is ever 100% safe. Check it yourself.

An ice-in date is when the lake freezes over and the ice cover stays through winter, as the DNR defines it for its citizen observers. It is not the day the ice will hold you. First ice can be thin, uneven and hidden under snow. Foot travel needs at least 4 inches of clear ice, according to the DNR. Snowmobiles and small ATVs need 5 to 7 inches. Those are minimums, not promises.

Mille Lacs ice-in dates, year by year

This table is every Mille Lacs ice-in date in the DNR record. Years not listed have no entry. That includes 2015 and 2023, and every year from 1981 to 1987, 1989, 1991 to 1993, 1995, 1997 to 2000, 2002 to 2013.

Source: Minnesota DNR State Climatology Office, Lake Ice In/Out Report for Mille Lacs (lake ID 48000200). The 2001 date is credited in the DNR data to the Minnesota Pollution Control Agency. The 2014 date appears twice in the DNR file, once from each of two sources, with the same date. We count it once.

How we read the numbers

Record length. The DNR file for Mille Lacs has 18 rows. One is a duplicate. That leaves 17 years, from 1979 to 2025.

Typical date. The DNR reports a median ice-in date "since 1950" of December 3 for Mille Lacs. We also checked it ourselves. We took the 17 distinct dates in the table above and found the middle one. It is also December 3. The average of the same 17 dates lands on December 3 too.

The spread. The gap between the earliest and latest date is 33 days. Of the 17 years:

• 4 froze before December 1 (1988, 1996, 2014, 2018).
• 11 froze from December 1 to December 7.
• 2 froze after December 7 (2001 and 2016).

So a first week of December lock-up is the usual outcome. Late November and mid-December both happen.

What the data cannot tell you. The record has gaps. We do not know the ice-in date for years with no entry. The DNR also says the dates should not be used to judge current ice thickness. The DNR does not post ice-in dates for the current year in real time, for safety reasons. This guide does not list a 2026 date because none is posted.

What affects freeze-up on Mille Lacs

We can only point to what the sources say. Mille Lacs is the second largest lake entirely within Minnesota, at 132,516 acres, according to the DNR's Minnesota facts list. That is a lot of open water for wind to work on. The DNR lists its maximum depth at 42 feet.

The DNR's ice safety page says ice strength depends on many factors. These include water depth under the ice, size of the water body, currents and local weather. It also says snow insulates the ice and slows the freezing process. We do not have a sourced lake-specific model of how wind and depth set the Mille Lacs freeze date, so we will not claim one. Use the table as a guide to timing, then check the ice itself.

Pressure ridges and moving ice

The DNR says pressure ridges form when ice expands and contracts with air temperature swings. It says ridges can range from a few inches to over 10 feet high, and can form in a matter of hours. Its advice: "Pressure ridges are always dangerous." Talk to local experts about known ridges. Watch for new ones.

Wind can move ice on a lake this size. In May 2013, sustained winds near 20 mph with gusts near 40 mph shoved ice from Mille Lacs onto shore. MPR News reported ice drifts 5 to 20 feet high that damaged boat houses and condos. That was late-season ice, not first ice. It shows how far a big ice sheet can travel when the wind pushes it.

DNR ice thickness minimums

From the DNR ice thickness guidelines for new, clear ice:

The DNR notes ice is seldom the same thickness across a lake. It can be a foot thick in one spot and an inch or two a few feet away. It also says new ice is usually stronger than old ice, and ice over moving water is often dangerous. The DNR does not measure ice thickness on Minnesota lakes. Your safety is your responsibility.

How to check ice this season

1. Do not go out on first ice because a date in a table says it froze.
2. Measure. Drill or chop a hole and check thickness often as you move.
3. Look at the ice. Clear ice is the standard the DNR numbers use. Snow cover hides cracks and slows freezing.
4. Stay off ridges, cracks that are moving, and areas near current.
5. Tell someone where you are going and when you will be back.

For current conditions, use local reports and your own measurements. Treat any report as a lead, not a green light.

No ice is ever 100% safe. Check it yourself.

FAQ

When does Mille Lacs usually freeze over?

Around December 3. That is the DNR median ice-in date for the lake.

What is the earliest Mille Lacs has frozen?

November 19, in 1996, in the DNR record that starts in 1979.

What is the latest Mille Lacs has frozen?

December 22, in 2001, in the same record.

Is Mille Lacs safe once it has frozen?

Not automatically. Ice-in only means the lake first froze. The DNR says there is no such thing as 100 percent safe ice. Check thickness yourself. The DNR minimum for foot travel is 4 inches of clear ice.

How thick does ice need to be for a snowmobile?

The DNR says 5 to 7 inches of clear ice for a snowmobile or small ATV. Side-by-sides need 7 to 8 inches.