As of 2020, the population was 218,245 and in 2023, that number increased to 232,439, making it the third largest county in the Jacksonville metropolitan area.

[6] This transformation has come as workers from Jacksonville, and to a smaller extent other nearby cities such as St. Augustine and Gainesville, have moved into newly built residential subdivisions.

[6] With the population expected to surpass 300,000 residents by 2040, projects such as the First Coast Expressway are being constructed to alleviate chronic congestion on major roadways in the county such as Blanding Blvd and U.S.

[7] Clay County is known for its rich military history with major current and former installations such as Branan Air Field, Naval Air Station Green Cove Springs, and Camp Blanding all being located in the county.

Black Creek begins at the St. Johns River just north of Green Cove Springs and runs through the central portion of the county.

Steamboats brought them to various hotels in Green Cove Springs, such as the St. Elmo, Clarendon, and Oakland.

President Grover Cleveland was the most prominent of such tourists and had spring water shipped to the White House.

Tourism later waned because of Henry Flagler's extension of the Florida East Coast Railway to other destinations such as Palm Beach and Miami.

Although Lee Field closed in the early 1960s, Camp Blanding continues to operate today as a base for military training.

[10] The southwestern portion of the county features many lakes which contribute to the Floridan Aquifer and are an important source of water for the surrounding region.

During the 2000s, high growth rates in Northeast Florida caused many of the lakes to dry up as demand for water increased.

The ten largest reported ancestry groups in the county were Irish (11.7%), English (11.6%), German (10.7%), American (4.7%), Italian (3.5%), Scottish (3.1%), French (2.2%), Polish (1.9%), European (1.5%), and Scotch-Irish (1.1%).

In total, 6.1% of residents were foreign-born with over 68% being naturalized citizens and the majority entering the United States prior to 2010.

Clay County is located in Florida's 6th Senate District represented by Republican Jennifer Bradley.

Florida House District 20 covers the central and southern parts of the county and is represented by Republican Bobby Payne.

According to the Florida Department of State, Republicans account for a majority of registered voters in Clay County.

[30] Due to their efforts, the first public library in Clay County was opened in 1961 in Green Cove Springs.

[30] The Green Cove Springs Library purchased a bookmobile in 1962 and began to provide outreach services to different areas within Clay County that same year.