Casner Township is one of sixteen townships in Jefferson County, Illinois, USA. As of the 2010 census, its population was 1,239 and it contained 510 housing units.

According to the 2010 census, the township has a total area of 36.02 square miles (93.3 km), of which 35.98 square miles (93.2 km) (or 99.89%) is land and 0.04 square miles (0.10 km) (or 0.11%) is water. The township is centered at 38°21'N 89°5'W (38.349,-89.088). It is traversed east–west by Interstate Route 64 and State Route 15.

• Woodlawn

• Jefferson City at 38°22′44″N 89°02′35″W / 38.379°N 89.043°W / 38.379; -89.043
• Roaches at 38°19′30″N 89°04′34″W / 38.325°N 89.076°W / 38.325; -89.076

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

• Grand Prairie Township (north)
• Rome Township (northeast)
• Shiloh Township (east)
• McClellan Township (southeast)
• Blissville Township (south)
• DuBois Township, Washington County (southwest)
• Ashley Township, Washington County (west)
• Richview Township, Washington County (west)
• Irvington Township, Washington County (northwest)

The township contains these three cemeteries: Locust Grove, Mount Catherine and Randolph.

• Interstate 64
• Illinois Route 15

Historical population

Census	Pop.	Note	%±
2016 (est.)	1,233
U.S. Decennial Census

• Illinois' 19th congressional district
• State House District 107
• State Senate District 54

• "Casner Township, Jefferson County, Illinois". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved January 17, 2010.
• United States Census Bureau 2007 TIGER/Line Shapefiles
• United States National Atlas

• City-Data.com
• Illinois State Archives