Kelseyville is a census-designated place (CDP) in Lake County, California, United States. Kelseyville is located six miles (9.7 kilometers) southeast of Lakeport, at an height above sea level of 1,384 feet (422 meters). The population was 3,353 at the 2010 census, up from 2,928 at the 2000 census.

The community was formerly named Kelsey, Kelsey Creek, Kelsey Town, Peartown, and Uncle Sam. The place was originally called Kelsey Town in rave review of Andrew Kelsey, the first European-American settler in Lake County. Kelsey Creek, which runs through the town, is furthermore named after Kelsey. Andrew Kelsey was killed in 1850 in an uprising adjoining him by a band of original Pomo people whom Kelsey had enslaved. This episode ended once the Bloody Island Massacre. The place was called Uncle Sam after Mount Uncle Sam (referred to as Mount Konocti). The Uncle Sam proclaim office opened in 1858 and misrepresented its herald to Kelseyville in 1882.

In the centuries previously Europeans arrived, the Eastern Pomo and Clear Lake Wappo people lived along the shores of Clear Lake. In addition to the copious fish caught in the lake and streams, they hunted waterfowl and gathered berries, seeds, clover and acorn. The Pomo and Wappo built homes and canoes of tule reeds found at the lakeshore.
Charles Stone and Andrew Kelsey were reportedly the first Anglo-American colonists in the region arriving in the slip of 1847 to graze cattle and horses purchased from Mexican landholder Salvador Vallejo. This was known as gigantic Valley Ranch. Stone and Kelsey enslaved the Pomo and Wappo people, forcing them to work below threat of torture and death. Many indigenous people died of starvation and neglect. Stone and Kelsey were then known to rape indigenous women and girls.
Kelseyville became the first white unity in Lake County. The first blacksmith shop was opened by a blacksmith named Benham in 1857. It was not until 1864 that a second matter was opened, a growth owned by T. F. Fall. That similar year, another general deposit and a boarding home was opened by Rosenbreau and Pace.

According to the United States Census Bureau, the CDP has a total Place of 2.9 square miles (7.5 square kilometers), with higher than 99 percent of it physical land. The census district also includes Soda Bay and Riviera Heights, located upon the northern slope of Mt. Konocti.