Chelan County (see map below) was formed from parts of Kittitas and Okanogan Counties after it was agreed that necessary travel to the Kittitas County seat in Ellensburg during winter months was not possible. Thanks to the efforts of Frank Reeves and Arthur Gunn, Chelan County was formed on March 13, 1899. Named after Lake Chelan, Chelan was orignally spelled "Tsill-ane" and is the name of a tribe of Salishan Indians who inhabited the shores of Lake Chelan in the 19th century.  The county was named from the writings of fur trader, Alexander Ross. Ross authored "Adventures of the First Settlers on the Oregon or Columbia River" and mentions Tsill-ane, as called by the natives "in a lake not far distant". This book can be read online or downloaded as a PDF file here.

 According to US Census Bureau estimates in 2020, the county population was about 76,229 and is ranked 17th most populous out of the state's 39 counties. The county seat is in the city of Wenatchee, located in the north-central part of Washington state at the confluence of the Columbia and Wenatchee Rivers and near the eastern foothills of the Cascade Mountain Range. Wenatchee is referred to as the "Apple Capital of the World" due to the valley's many orchards. Wenatchee is also sometimes referred to as the "Buckle of the Power Belt of the Great Northwest" because of a series of hydroelectric dams built on the Columbia River.

The city of Cashmere has been acknowledged as the geographical center of the state, located at the foot of the Cascade Mountains. It was first inhabited in 1881 by a German immigrant. In 1889 a post office named Mission was established. In 1892, the town began to form and a general store was opened. The name Mission was changed to Cashmere after the mountainous Vale of Kashmir in northwest India, and the town was incorporated July 1, 1904. Cashmere is well known for being the home of Aplets and Cotlets, an internationally famous fruit candy.

The city of Chelan (sometimes referred to as Lake Chelan) is known as a recreational mecca, heavily populated during summer months by tourists. But it was gold, silver, and copper that first  brought settlers to the area as well as an abundance of Ponderosa pine, Douglas fir and plenty of pure alpine water. The Lakeside settlement begin to form in the late 1880s. A post office was established in 1890, then general stores, a hardware store, drug store, dentist, saloons, and a blacksmith opened up the following year. In 1893 there was a failed attempt to incorporate the town of Chelan but by May 1902 it was voted to incorporate the town.

The city of Entiat is nestled between Wenatchee and Chelan at the confluence of the Entiat and Columbia rivers. This area of the Columbia River is known as Lake Entiat. The Entiat Valley was first settled by the Columbia River Chinook Indian tribe in the 1800s and was named Enteatqua, meaning "rapid water". The head of the tribe, Chief Moses, in 1884 agreed to move with his people to the Colville Reservation. Today 12 tribes, including the Wenatchi, Chelan, and Entiat, make up the Federated Tribes of the Colville Reservation. Due to being difficult to reach, the first white settler to the Entiat Valley didn't arrive until 1887, with the first public school established in 1891. The Entiat Post Office opened in 1895. The town officially incorporated in 1944. When the Rocky Reach Dam was completed downriver in about 1960, much of Entiat had to be relocated to higher ground because of rising waters.

Leavenworth, first known as Icicle Flats in 1885 due to the location at the confluence of the Wenatchee River and Icicle Creek, is surrounded by mountain peaks and bountiful land where salmon was plentiful and the deer and elk were hunted by the Yakima, Chinook, and Wenatchi tribes. Settlers came looking for gold, timber, and furs. By 1893 the town was platted and named for Captain Charles Leavenworth. A rail line was built and the logging and sawmill industry boomed, until the 1920s when the railroad was re-routed, bypassing Leavenworth and almost causing it to became a ghost town. The stock market crash of 1929 caused the economy tofurther spiral downward. With stores closing and people leaving, in 1962 the community came up with the idea of reinventing Leavenworth with a Bavarian theme. They remodeled buildings, all with private money, making Leavenworth into the premier tourist destination it is today.

Wenatchee, the county seat, is located midway between Seattle and Spokane. Its name comes from the nomadic, indigenous Wenatchi tribe and has been said to mean "a river and its valley". Wenatchee sits at the confluence of the Wenatchee and Columbia rivers and is noted as the Apple Capital of the World. The first non-Native American settlers were gold prospectors, Chinese miners, cattlemen, and missionaries. It was founded in 1888. In 1892 the Great Northern Railway built its train depot a mile south of Wenatchee and the town was incorporated in 1893. The 1900 US Census counted 451 residents. As of 2020 there were an estimated 35,140 people counted.