Laenna Township is located in Logan County, Illinois. As of the 2010 census, its population was 584 and it contained 282 housing units.
According to the 2010 census, the township has a total area of , of which (or 99.94%) is land and (or 0.06%) is water.
The township includes the geographical center of the State of Illinois, a small monument to which has been erected at 40ð3.157'N 89ð11.087'W (40.05259,-89.18482), in a park southeast of Melvin Street and East Olive Street in the village of Chestnut.