1899-1905 - Frederick & Middletown Railway Co.
1905-1909 - Frederick & Middletown Railroad Co.
1904-1909 - Myersville & Catoctin Railway Co. (to Middletown)
1907-1909 - Jefferson & Braddock Heights Railway Co. (to Middletown)
1909-1913 - Frederick Railroad Co.
1902-1908 - Hagerstown & Boonsboro Railway Co.
1906-1908 - Hagerstown & Northern Railroad Co. (to Shady Grove PA)
1907-1908 - Hagerstown & Myersville Railway
1908-1913 - Hagerstown Railway Co.
1913-1923 - Hagerstown & Frederick Railway Co.
1923-1954 - Potomac Edison Co.
Interurban lines:
Frederick-Middletown (1899-1945)
Middletown-Myersville (1904-1945)
Middletown-Jefferson (1907-1940)
Hagerstown-Boonsboro (1902-1938)
Hagerstown-Shady Grove PA (1906-1932)
Hagerstown-Myersville (1907-1938)
Hagerstown-Williamsport (1907-1947)
Frederick-Thurmont (1910-1954)
Replacement interurban bus service operated most years by Blue Ridge Transportation Co.