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.

92.9% spoke English, 3.4% Hmong, 1.1% German and 1.1% Spanish as their first language.

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.