Marion Township is one of 20 townships in Allen County, Indiana, United States. As of the 2010 census, its population was 3,858.

In September, 1834, the Commissioners of Allen County created Root Township, which embraced all of present-day Marion Township, as well as a portion of present-day Adams County. Adams County was created on February 7, 1835, leaving only a portion of Root Township still in Allen County. In August, 1835, this remainder of Root Township was reorganized and renamed Marion Township.

According to the United States Census Bureau, Marion Township covers an area of 34.88 square miles (90.35 km); of this, 34.65 square miles (89.75 km) is land and 0.23 square miles (0.59 km), or 0.66 percent, is water.

• Hessen Cassel at 40°58′40″N 85°04′45″W / 40.977826°N 85.079136°W / 40.977826; -85.079136
• Poe at 40°56′09″N 85°05′13″W / 40.935881°N 85.086914°W / 40.935881; -85.086914
• Soest at 40.996157°N 85.037435°W

(This list is based in part on USGS data and may include former settlements.)

• Adams Township (north)
• Jefferson Township (northeast)
• Madison Township (east)
• Root Township, Adams County (southeast)
• Preble Township, Adams County (south)
• Jefferson Township, Wells County (southwest)
• Pleasant Township (west)
• Wayne Township (northwest)

The township contains the following cemeteries: Antioch Lutheran, Bethel Baptist (defunct), Coleman family (defunct), Emmanuel Lutheran, Hall (disappeared), Morton family (defunct), Poe/Williamsport, St. John's Lutheran (defunct), St. Joseph Hessen Cassel Roman Catholic, St. Paul's Lutheran (defunct), and Thompson family (defunct).

• I-469 (Ronald Reagan Expressway)
• US 24
• US 27
• US 33

• St. Marys River

• East Allen County Schools

• Indiana's 3rd congressional district
• State House District 79
• State Senate District 19

• United States Census Bureau 2008 TIGER/Line Shapefiles
• United States Board on Geographic Names (GNIS)
• IndianaMap