Old Rappanannock County, Virginia is so styled to distinguish it from the modern day Rappahannock County, Virginia.
Old Rappahannock County was formed from Lancaster County on 11 December 1656. It functioned as a county until 1692, when it was abolished and split into Essex County and Richmond County. At the same time, Farnham Parish was divided into North Farnham Parish (Richmond County) and South Farnham Parish (Essex County.) The Rappahannock County records were retained by Essex County. The main reason for the division was the physical separation of the two jurisdictions by the Rappahannock River.
An anomaly of this division was that the parent county, and its court, were abolished entirely and substituted by two new counties and two new parishes.