Douglas County is lightly wooded, mostly with ponderosa pine, with broken terrain characterized by mesas, foothills, and small streams.

Senator Stephen A. Douglas[4] of Illinois, who died five months before the county was created.

The county seat was originally Franktown, but was moved to California Ranch in 1863, and then to Castle Rock in 1874.

Parts of the county lie within the Pike National Forest and were crossed by the historic South Platte Trail.

If filled to capacity, surface size would be 1,140 acres, making this a fairly significant reservoir in Colorado and Douglas County's largest body of water.

The area is host to a variety of animals and the Cherokee Ranch petrified forest.

The Prairie Canyon Ranch, at 4620 CO-83, about 10 miles (16 km) south of Franktown, is a Douglas County Open Space.

It is a working cattle ranch on 978 acres (3.96 km2), open to the public on special events.

The median income for a household in the county was $82,929, and for a family was $88,482 (these figures had risen to $93,819 and $102,767, respectively, as of a 2007 estimate[16]).

In 2008, it ranked eighth in the United States in that category; it was one of two in the top 15 not in the vicinity of New York or Washington.

In 2020, Joe Biden achieved the highest vote share for a Democratic presidential nominee in the county since 1964.

[18] In 2022, incumbent Democratic governor Jared Polis lost the county by a razor-thin margin, winning nearly 49% of the vote.

The library also houses the Douglas County History Research Center, which collects and preserves the history of Douglas County, the High Plains, the Divide area of the Front Range and the State of Colorado, to provide historical research resources to the public.