State Route 315 passing over the Olentangy in Columbus in 2002
|Origin||~ 2 mi (3.2 km) North east of Galion.|
|Mouth||Scioto River at Columbus|
|Source elevation||~ 1,190 ft (363 m) |
|Mouth elevation||~ 710 ft (216 m) |
|Basin area||543 mi² (1,046 km²) |
It was originally called keenhongsheconsepung, a Delaware word literally translated as "stone for your knife stream", based on the shale found along its shores. Early settlers to the region translated this into "Whetstone River". In 1833, the Ohio General Assembly passed legislation intending to restore the original Native American names to some Ohio waterways, but mistakenly gave Whetstone River the name "Olentangy"—Delaware for "river of the red face paint"—which had actually belonged to what is now known as Big Darby Creek.
The Olentangy River rises in Crawford County approximately 2 mi (3.2 km) northeast of Galion, flowing through Galion and northwest towards Bucyrus, where it then turns south and flows through Eastern Marion County, Ohio (where it is still locally known as the Whetstone River) before flowing south into Delaware County. The river continues southward towards the communities of Delaware, Powell, Worthington, and the village of Riverlea, before reaching Columbus and the campus of the Ohio State University, before joining with the Scioto River in downtown Columbus.
The Delaware State Park Reservoir, also known as Delaware Lake, was constructed along the Olentangy River in 1951. The reservoir is located 5 miles north of the city of Delaware, and was built by the U.S. Army Corps of Engineers for flood control purposes. On January 13, 2005, Delaware Dam was nearly overtopped. The water level came within less than 1 foot of requiring the main spill gates to be opened before it began dropping.
The Olentangy River is the primary source of drinking water for much of Delaware County. Both the City of Delaware and Del-Co Water Company, the supplier of drinking water to most of rural Delaware County (and other communities beyond), draw the majority of their water supplies from the Olentangy system.
Twenty-two miles of the Olentangy have been designated a State Scenic River by the Ohio Department of Natural Resources, Division of Natural Areas & Preserves.
Variant names 
- Whetstone Creek
- Whetstone River
- Whitestone Creek
- U.S. Geological Survey. Blooming Grove quadrangle, Ohio. 1:24,000. 7.5 Minute Series. Washington D.C.: USGS, 1988.
- U.S. Geological Survey. Southwest Columbus quadrangle, Ohio. 1:24,000. 7.5 Minute Series. Washington D.C.: USGS, 1995.
- "Map of Ohio watersheds".
- "The National Map". U.S. Geological Survey. Retrieved Feb. 14, 2011.
- "Delaware Dam nearly overtopped on January 13, 2005".
- "Olentangy State Scenic River".
- U.S. Geological Survey Geographic Names Information System: Olentangy River
- Friends of the Lower Olentangy Watershed
- Delaware Dam level and outflow graph
- Olentangy River Level Gauge at Worthington, OH