First authored by OConnor

The Frederick and Pennsylvania Line railroad ran from Frederick, Maryland to the Pennsylvania-Maryland State line, or Mason–Dixon line near Kingsdale, Pennsylvania consisting of 28 miles (45.1 km) of center-line track and 29.93 miles (48.17 km) of total track including sidings. Chartered in 1867, the railroad started construction in 1869 and cost $868,687.50.

It opened October 8, 1872 and was subsequently leased to the Pennsylvania Railroad (PRR) from January 1, 1875 and in July of that year, PRR formed the Frederick Division to operate the rail line. In the spring of 1896, it was liquidated in a judicial sale to the PRR for 10 percent of its 1896 book value.

Pennsylvania reorganized the railroad in December, 1896 as the Frederick and Northern Railroad Company. In March 1897, this new company was itself merged with other PRR-controlled railways, the Littlestown Railroad Company and the Hanover and York Railroad Company into the York, Hanover and Frederick Railroad, chartered under the general laws of Pennsylvania and Maryland. In 1914, this railroad and the newly built Central Railroad of Maryland were then merged into the York, Hanover and Frederick Railway Company which remained a wholly owned stock subsidiary of the PRR into the creation of the PennDel Company on December 31, 1953,[1] and then the Penn Central Transportation Company merger in 1968 and then bankruptcy in 1970. The Frederick and Pennsylvania Line segment and other former PRR properties in Maryland were sold by Penn Central to the State of Maryland in 1982 for $9,295,000.[2] In 2006, the State sold approximately 20 miles of the branch to the Maryland Midland Railroad for approximately $300,000.[3]

As of 2021, all but two miles (3.2 km) at the southern terminus at Frederick still exist, operated by either the Walkersville Southern Railroad or the Maryland Midland Railway.