It flows generally north for its first 25 miles (40 km) into eastern Hancock County, where it turns sharply to the west.

It joins the Auglaize from the east in western Putnam County approximately 2 miles (3 km) north of Cloverdale at 41°02′29″N 84°17′57″W / 41.041483°N 84.299245°W / 41.041483; -84.299245.

In 1908, Tell Taylor wrote "Down by the Old Mill Stream", a popular song of the early 20th Century and a barbershop favorite, while sitting on the banks of the Blanchard River.

Around 1939 numerous projects by the Works Progress Administration improved the river near Findlay, including construction of two major bridges, clearing substantial existing pollution, and building a sewage treatment plant to reduce ongoing pollution.

On November 28, 2012, officials from Hancock and Putnam counties traveled to Washington D.C. to lobby for $1.7 million in federal funding to complete phase three of the Blanchard River Flood Mitigation study.