During the second half of the 18th century, Frederick County bounded more land than any other county in Provincial Maryland, fully 551,273 acres. It encompassed all of the current counties of Frederick, Garrett, Allegany, Washington, and Montgomery and parts of Howard and Carroll, and some land in Pennsylvania prior to the drawing of the Mason-Dixon Line (1763/1767). These facts go a long way to explain why the Frederick County coverage in Vernon L. Skinner Jr.'s series "Abstracts of the Debt Books of the Provincial Land Office of Maryland" runs to six volumes. This is the fourth volume in that series. The information in this series is presented in a tabular form as follows: liber and folio citation, with any pertinent date; name of the person paying the taxes; and name of the tract of land and amount of acreage. Each Frederick County volume is indexed by the name of the land owner and his/her track, and, on average, each volume identifies about 10,000 parcels of land.