Marnoo is a rural town on the Wimmera Highway between Horsham and St Arnaud. It is one of several wheat growing towns east of Horsham, including Murtoa and Rupanyup.
Marnoo was named after a pastoral run taken up in 1845 by Martin Shanahan, a pastoralist who followed the Richardson River until he found suitable grazing land. His homestead was near the junction of the river and Wallaloo Creek. It is thought that the name ‘Marnoo’ was derived from an Aboriginal word meaning finger or hand.