On July 4, 1760, Maryland and Pennsylvania settled the boundary dispute between the two provinces with the signing of an elaborate document. The final settlement came with the acceptance of the Mason-Dixon Line in 1767, which took a large portion of land previously claimed by Maryland (and Pennsylvania) and added it to Pennsylvania.
[from John Ashbury's History Moments]

WESTERN MARYLAND

• 1728 - Western Half
• 1728 - Eastern Half

• 1741 - Western Maryland

• 1744 - Western Half
• 1745 - Eastern Half
  

• 1749 - Western Half
• 1749 - Eastern Half
  

• 1763 - Western Half
• 1763 - Eastern Half
  

• 1776 - Washington County
• 1776 - Frederick County
• 1776 - Montgomery County

• VA & MD & PA
  • Early 1700's - Old Wagon Roads & Ferries

• JEFFERSON CO, WV (previously VA)
  • 1809 - w/ Berkeley and Frederick Counties
  • 1852 - Districts & Landowners
  • 1883 - Districts & Landowners

• LOUDOUN Co, VA
  • 1860's - also surrounding counties
  • 1864 - & Jefferson Co, WV - Landowners

• ADAMS CO, PA
  • 1821 - Adams & York County
  • 1858 - Townships & Landowners
  • 1872 - Townships & Landowners

• FREDERICK COUNTY
  
  • 1830 - Districts
  • 1854 - Districts & Towns
  • 1858 - Isaac Bond Map
  • 1872-1881 - Districts
  • 1873 - Frederick & Carroll Counties
  • 1895 - Rand McNally
  • 1979 - USGS
    Frederick City
    • 1858 - w/ old graveyards
    • 1887 (Sanborn)

• CARROLL COUNTY
  • 1837 - Districts
  • 1862 with Landowners
  • 1863 with Landowners
  • 1873 - Carroll & Frederick Counties
  • 1880 Districts
  • Current Districts
    • Westminster       1887       1892       1897
    • Taneytown           1887
    • Mount Airy         1899

• WASHINGTON COUNTY
  • 1808 - Districts
  • 1859 - Districts with Landowners
  • 1873 - Districts
  • 1877 - District Maps with Landowners
  • 1877 - Atlas

• ALLEGANY & GARRETT COUNTIES - 1873

• MONTGOMERY COUNTY
  • 1862 - also Washington, DC
  • 1865 - Districts & Landowners
  • 1873 - Montgomery & Howard Counties
  • 1879 - Montgomery County

• BALTIMORE COUNTY - 1857
  • Baltimore City - 1804
  • Baltimore City - 1876

• BALTIMORE & HARFORD COUNTIES - 1873

• WASHINGTON, DC - 1851

• Maryland Place Names

• Maryland GenWeb County MAP

• County Formations (page down for interactive map)

• State Formations

• Historic Map Works - Search Box

• Google Maps