Lost River Township is one of six townships in Martin County, Indiana, United States.

As of the 2020 census, its population was 513 and it contained 250 housing units.

[2] According to the 2010 census, the township has a total area of 42.75 square miles (110.7 km2), of which 42.29 square miles (109.5 km2) (or 98.92%) is land and 0.46 square miles (1.2 km2) (or 1.08%) is water.

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

The township contains these seven cemeteries: Anderson, Cornel, Emmons Ridge, Green, Jones, Simmons and Walker.