Avoca Township is located in Livingston County, Illinois. As of the 2010 census, its population was 405 and it contained 149 housing units.
The township is named after the former community of Avoca, settled in 1832 by William (1785–1834) and Sarah McDowell (1787–1858) and their seven children. The Avoca post office was established on 7 June 1838, and community was laid out in 1854. A church (the Pioneer Church) was built in the settlement in 1856. After the railroad bypassed the settlement, the buildings were dismantled and moved away, and the church burned down in 1876. A new church known as the Centennial Church was built the same year but dismantled in 1910. Today only the churchyard cemetery remains.
According to the 2010 census, the township has a total area of 36.41 square miles (94.3 km2), of which 36.31 square miles (94.0 km2) (or 99.73%) is land and 0.1 square miles (0.26 km2) (or 0.27%) is water.