[3][4][5][6] On a trip through eastern Virginia, the German-born Miller had heard reports about a lush valley to the west which had been discovered by Governor Alexander Spotswood's legendary Knights of the Golden Horseshoe Expedition, and then moved his family down from Lancaster County, Pennsylvania.

[7][8][9] In 1741, Miller purchased 820 acres (3.3 km2), including a large lithia spring, near Elkton, Virginia, and lived on this property for the remainder of his life.

Rather than cross such a formidable physical barrier, most early settlers came southerly up the valley across the Potomac River from Maryland and Pennsylvania.

[13] The county is named for Charles Watson-Wentworth, 2nd Marquess of Rockingham, a British statesman (1730–1782).

He was Prime Minister of Great Britain twice, and a keen supporter of constitutional rights for the colonists.

During his first term, he brought about the repeal of the Stamp Act of 1765, reducing the tax burden on the colonies.

Appointed again in 1782, upon taking office, he backed the claim for the independence of the Thirteen Colonies, initiating an end to British involvement in the American Revolutionary War.

[citation needed] By 1778, it was unusual to honor British officials in Virginia, fighting for its independence.

[citation needed] However, long their political supporter in the British Parliament, the Marquess of Rockingham was a popular figure with the citizens of the new United States.

[14] In 1979 when the Adolf Coors Brewing Company came to Rockingham County it caused an uproar; some citizens thought it would corrupt the morals of the area while others wanted the new jobs.

Rockingham is bisected by another geographic formation, Massanutten Mountain, which stretches from just east of Harrisonburg, VA to a few miles southwest of Front Royal, VA in Warren County, VA. Massanutten Mountain splits the central Shenandoah Valley, as the German River and the North Fork Shenandoah River flow on its western side and the South Fork flows on the eastern.

On May 26, 2005, the RCSO was accredited by the Virginia Law Enforcement Professional Standards Commission (VLEPSC).

On September 9, 2021, the VLEPSC Executive Board granted re-accreditation status to the Rockingham County Sheriff's Office.