Jefferson Township is one of the seventeen townships of Logan County, Ohio. As of the 2020 census, the population was 3,028.

Several municipalities are located in Jefferson Township:
• The village of Zanesfield, in the south center
• Part of the city of Bellefontaine, in the west
• Most of the village of Valley Hi, in the south

Compared with most of western Ohio, Jefferson Township is quite hilly. Campbell Hill, the highest point in Ohio, is located inside the Bellefontaine city limits in western Jefferson Township. On the other hand, the Marmon Valley, which extends through the southern part of the township, is a small pass through the Bellefontaine and Bristlecone Ridges. The same forces that shaped the township's terrain also created Zane Shawnee Caverns, a cave system in the northeastern part of the township.

Jefferson Township contains the source of the Mad River, and a ski resort — unusual for western Ohio — is located near Valley Hi in the southern part of the township.