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.

Historical population

Census	Pop.	Note	%±
1890	1,448		—
1900	1,415		−2.3%
1910	1,283		−9.3%
1920	1,155		−10.0%
1930	858		−25.7%
1940	879		2.4%
1950	707		−19.6%
1960	610		−13.7%
1970	509		−16.6%
1980	524		2.9%
1990	449		−14.3%
2000	532		18.5%
2010	572		7.5%
2020	513		−10.3%
Source: US Decennial Census

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

• Rusk at 38°33′26″N 86°45′25″W / 38.557276°N 86.75694°W / 38.557276; -86.75694
• Windom at 38°34′26″N 86°47′52″W / 38.573942°N 86.797775°W / 38.573942; -86.797775
• Yenne at 38°32′52″N 86°47′37″W / 38.547831°N 86.793607°W / 38.547831; -86.793607

(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.

• U.S. Route 150

• Shoals Community School Corporation

• Indiana's 8th congressional district
• State House District 62
• State Senate District 48

• "Lost River Township, Martin County, Indiana". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved September 29, 2009.
• United States Census Bureau 2008 TIGER/Line Shapefiles
• IndianaMap

• Indiana Township Association
• United Township Association of Indiana
• City-Data.com page for Lost River Township