Big Walnut Creek starts near Mount Gilead, Ohio, in Morrow County.

It flows south to eastern Delaware County and parallels Alum Creek.

It passes to the east of Sunbury and into Hoover Reservoir, which then crosses into Franklin County.

From the dam outflow in Westerville the creek flows through Gahanna and Whitehall.

[5] According to the Geographic Names Information System, the Big Walnut Creek has also been known as:[6]