Littleton lies on the South Platte River in the Colorado Piedmont region of the Great Plains a few miles east of the Front Range of the Southern Rocky Mountains. Most of the city lies on the east side of the river. Several small tributaries of the river flow northwest through the city; from north to south, these include Big Dry Creek, Slaughterhouse Gulch, Lee Gulch, and Dad Clark Gulch. In addition, there are several small lakes and reservoirs located along the river in the southwestern part of the city. Immediately west of the river are Cooley Lake, Bufflehead Lake, South Platte Reservoir, Eaglewatch Lake, Redtail Lake, and Blackrock Lake. East of the river lie Wolhurst Lake and McLellen Reservoir which is fed and drained by Dad Clark Gulch. Chatfield Reservoir lies immediately southwest of the city.
As a suburb of Denver, Littleton is part of the Denver-Aurora metropolitan area and the Front Range Urban Corridor. It shares a border with Denver and Englewood on the north, Greenwood Village on the northeast, Centennial on the east, Highlands Ranch on the south, Columbine and Columbine Valley on the west, and Bow Mar on the northwest.