The Delaware River rises west of Sabetha, Kansas in Nemaha County. The river's course is generally southeast through the counties of Nemaha, Brown, Jackson, Atchison, and Jefferson in northeast Kansas. The Delaware passes through The Kickapoo Nation Reservation and is an important river for the tribe. Some of its main tributaries include Grasshopper Creek, Muddy Creek, Elk Creek, Straight Creek, Cedar Creek and Rock Creek.
The Delaware's course takes it through rich farmland and this gives the river's water a very muddy appearance. Just south of Valley Falls the river enters Perry Lake, a man made reservoir to control flooding. It then enters the Kansas River just north of Lecompton, Kansas. Some cities within 10 miles of the river include, Sabetha, Fairview, Powhattan, Horton, Whiting, Muscotah, Holton, Valley Falls, Ozawkie, Perry, and Lecompton, Kansas.
The river forms Perry Reservoir, which is a major regional lake for boating, swimming, camping, fishing and other activies. The river is also great for fishing, and some of the dominant fish of the river include channel catfish, flathead catfish, carp, longnose gar, drum, sauger, crappie, and white bass.