[5] The Mexican government issued a land grant to the first Anglo-American settler in the county, Thomas G. McGhee of Tennessee, in 1835.

The county is named for Tennessee native Captain John Coffee Hays[11] of the Texas Rangers.

[5] Camp Ben McCulloch, named after a brigadier general, was organized in 1896 for reunions of United Confederate Veterans.

[13] A teacher's college, Southwest Texas State Normal School, was established in San Marcos in 1899.

[15] The current Hays County Courthouse in San Marcos was erected in 1908 in Beaux-Arts style by architect C.H.

[17] Lyndon Baines Johnson graduated from Southwest Texas State Teachers College in 1930.

[19] San Marcos Army Air Field was renamed Gary Air Force Base in 1953 to honor Second Lieutenant Arthur Edward Gary, the first San Marcos resident killed in World War II.

[21] The county is predominantly in the Edwards Plateau, with the southeast portion in the Texas Blackland Prairies.

[citation needed] Higher education in Hays County includes one four-year institution, Texas State University, in San Marcos.

A Williams Institute analysis of 2010 census data found about 7.4 same-sex couples per 1,000 households in the county.

Hays County currently leans towards the Democratic Party in federal elections.

[36] Ann Richards in 1990 was the last Democratic gubernatorial candidate to win the county, when she took 56.6% of the vote that year, until 2018, when Lupe Valdez won with a 49.6% plurality.

[36] In the 2022 elections, Democrats won all but one race in Hays County; They flipped several countywide seats previously held by Republicans.

San Marcos, home of Texas State University, and the city of Kyle generally vote Democratic.

Driftwood, Dripping Springs, Wimberley, and Woodcreek generally vote Republican.