It is part of a watershed that drains a 1,757 square miles (4,550 km2) area in 11 southwestern Ohio counties: Clark, Montgomery, Madison, Greene, Warren, Butler, Clinton, Clermont, Brown, Hamilton, and Highland.

[8] The river's main tributary, the East Fork of the Little Miami,[9][10] was dammed in 1977 by the United States Army Corps of Engineers to create Harsha Lake, located in East Fork State Park.

[9] The river's headwaters, considered part of the North Fork, are located about 5 miles (8.0 km) from South Charleston in Clark County,[11] near Plattsburgh.

This 56-page booklet, illustrated with maps and black and white photographs, first presented the idea of a corridor of parks and natural areas along the river.

In June 1967 Dayton newspaper editor Glenn Thompson would bring together educator Arthur Morgan, business leader Charles Sawyer, and outdoor enthusiast Corwin Fred to form Little Miami Incorporated, dedicated to the preservation of the Little Miami River.

Mr. Thompson was the editor of the Dayton Journal-Herald in the late 1950s, and a strong advocate for the preservation of green space in the Miami Valley.

[16] The portion of Peters Cartridge Company factory on the opposite side of the river from Kings Mills in Hamilton Township, which closed in 1944 and is now owned by DuPont, was declared a Superfund site in 1996.

In September 2018, 15 acres of the 71-acre site was removed for the NPL after successful cleanup goals were achieved.

The river is protected by a number of nature preserves owned by Little Miami Inc., as well as by state and local parks (see below).