At that time the county stretched to the northern border with the Upper Peninsula of Michigan.

[3] Marathon County comprises the Wausau, WI Metropolitan Statistical Area and is included in the Wausau–Stevens Point–Wisconsin Rapids, WI Combined Statistical Area.

The Marathon County Park Commission has posted a geographical marker[5] that identifies the spot (45°N, 90°W) of the exact center of the northern half of the Western Hemisphere, meaning that it is a quarter of the way around the world from the Prime Meridian and halfway from the Equator to the North Pole.

As of the census[11] of 2000, there were 125,834 people, 47,702 households, and 33,868 families residing in the county.

23.60% of all households were made up of individuals, and 9.50% had someone living alone who was 65 years of age or older.

The Marathon County Public Library (MCPL) has its headquarters in downtown Wausau, Wisconsin.

Since 2016, Donald Trump has carried it by double-digit margins in all three of his campaigns.