It is located in the counties of Mille Lacs, Aitkin, and Crow Wing, roughly 75 miles north of the Minneapolis-St. Paul metropolitan area.

Mille Lacs Lake hosts numerous islands, many of which are an acre or smaller and are in private ownership.

Deep-water angling takes place on the southern deep gravel and rocks as well as on dozens of mud flats in the north half of the lake.

As late as 1843, it was referred to as "Mini Sagaigonin or Mille Lacs" on United States government maps.

[7] Mille Lacs Lake has an overall trophic state index (TSI) of 43, making it moderately mesotrophic.

[10] The presence of zebra mussels has reduced the trophic state index of the lake, with Secchi depth readings increasing noticeably since their arrival, likely due to their methods of filter feeding on suspended particles.

[10] A sharp rise in water transparency of the lake after the year 2010, measured via Secchi depth, coincides with the zebra mussel invasion timeline.

[14] In particular, the sediment core demonstrated the decline of bottom dwelling microbes in favor of microbial taxa that float freely in the water column, likely as a result of increased phosphorus availability within the pelagic zone of the lake.

Ground-water in the surrounding areas of Mille Lacs Lake occurs in glacial and bedrock aquifers.

[15] Upon inspection of this groundwater in the late 1990’s, sodium, manganese, and iron levels repeatedly exceeded acceptable EPA standards for health and drinking water.

[15] Multiple common pesticides, trace metals, and volatile organic compounds were also found in samples, but were below detection limits, except for zinc levels.

[15] Possible sources of groundwater contamination within lakes due to anthropogenic effects can include but are not limited to land usage and commercial, industrial, and agricultural activities.