William Smith purchased the Blenheim lands in 1712. The nephew of Sarah Churchill, the first duchess of Marlborough, he named the property after Churchill's estate in Oxfordshire. The Smith children married into both the Pacas of Abingdon and the Gileses of Mount Pleasant and became prominent citizens throughout Harford County.

The family is connected to Aquila Paca, a signer of the Bush Declaration, the first declaration of independence from an organized group of citizens. One year later, in 1776, Paca's uncle, William Paca, signed the Declaration of Independence. 

In 1795, William Smith died, leaving Blenheim to his son, Paca Smith. Since Paca and his sister Frances were both minors, they were placed in the care of Samuel Hughes, the owner of Mount Pleasant, who began to squander the siblings' fortune until they threw him out when they came of age. 

Christopher Weeks, historian and author of An Architectural History of Harford County, writes that Paca was a learned scholar and successful lawyer, an intellectual with a "Jeffersonian love of liberty and learning." His personal library at Blenheim contained over 400 volumes, and his walls were covered with maps. Paca's will not only freed his remaining slaves but also provided them with clothing and money.

Upon his death, Paca instructed his heirs to spend "as much money as will pay my funeral expenses and bury me decently along side of my wife at my place called Blenheim." Paca and his wife Sarah Knight Smith are both buried in the Blenheim cemetery.  Without any children, Gustav Smith, Paca's nephew, inherited the estate and sold it to Dr. William Sappington in 1831.