ADAMS COUNTY : created on January 22, 1800, from part of York
county. Gettysburg is the county seat, and was incorporated  Mar. 10
1806.
ALLEGHENY COUNTY: created  September 24, 1788, from
parts of Westmoreland and Washington counties. Pittsburgh, the county seat, was incorporated on. April 22,1794 and became a city on March 18, 1816.

ARMSTRONG COUNTY: created on March 12, 1800, from parts
of Allegheny, Westmoreland, and Lycoming counties. It was administratively attached to Westmoreland County until 1805. Kittanning, the county seat, was incorporated on April 2, 1821.

BEAVER COUNTY: created on March 12, 1800, from parts of
Allegheny and Washington counties,. It was administratively attached to Allegheny County until 1803. Beaver, the co.seat, was incorporated on March 29,  1802.

BEDFORD COUNTY: created on March 9, 1771, from part of Cumberland
County.  Bedford, the county seat, was incorporated,  March l3, 1795.

BERKS COUNTY: created on March 11, 1752, from parts of
Philadelphia, Chester, and Lancaster counties.  Reading, the county seat, was incorporated on September 12, 1783 and as a city on March 16, 1847.

BLAIR COUNTY: created on February 26, 1846, from parts of
Huntingdon and Bedford counties. Hollidaysburg. the county seat.was
incorporated 11 August 10, 1836.

BRADFORD COUNTY: created on February 21, 1810, from parts
of Lucerne and Lycoming counties, and named Ontario County.
On March 24,  1812, it was renamed for William Bradford, second Attorney General of the United States. Towanda, the county seat, was incorporated on March 5. 1828.
 
BUCKS COUNTY: One of the three original counties created by
William Penn in November, 1682.  Doylestown replaced Newtown as the county seat in 1812, and was incorporated on April 16, 1838.

BUTLER COUNTY: created on March 12, 1800, from part of
Allegheny County and named for General Richard Butler. It was at-
tached to Allegheny County until 1803. Butler., the county seat,  incorporated on February 26, 1817, and became a city on .January 7, 1918.

CAMBRIA COUNTY: created on March 26, 1804, from parts of
Huntingdon, Somerset, and Bedford counties. It remained administratively attached to Somerset County until 1807. Ebensburg, the county was incorporated on January 15, 1825.

CAMERON COUNTY: created on March 29, 1860, from parts of
Clinton, McKean, Elk, and Potter counties. Emporium, the county seat, was incorporated on October 13, 1864.

CARBON COUNTY: created on March l3, 1843, from parts of
Northampton and Monroe counties  Jim Thorpe, the county seat, was incorporated as theborough of Mauch Chunk on January 26, 1850. It was renamed
in 1954.

CENTRE COUNTY: created on February l3, 1800, from parts of
Huntingdon, Lycoming, Mifflin, and Northumberland counties.
Bellefonte, the county seat. was incorporated on March 28, 1806 .

CHESTER COUNTY: one of the three original counties created by
William Penn in November, 1682. West Chester, the county seat,
was incorporated on March 28, 1799.

CLARION COUNTY: created on March 11, 18S9, from parts
Venango and Armstrong counties, Clarion, the county seat, was
incorporated  April 6, 1841.

CLEARFIELD COUNTY: created on March 26, 1804, from parts.
Huntingdon and Lycoming counties. For many years Clearfield County
was functionally  part of Centre County, electing its first commissioners
in 1812.  It was organized for judicial reasons in 1822.  Clearfield, the county seat, was incorporated April 21, 1840.

CLINTON COUNTY: created on June 21, 1899, from parts
Centre and Lycoming counties.  Lock Haven, the county seat, was incorporated on
May 25, 1840, and incorporated as a city on March 28, 1870.

COLUMBIA COUNTY: created on March 22, 18l3, from part Northunberland County;   Bloomsburg,  county seat after November 30, 1847, was incorporated as a town on March 4. 1870.   Danville. the county seat from 1813 to 1846 became the county seat of Montour County.

CRAWFORD COUNTY: created on March 12, 1800. from part
Allegheny County. Meadville, the county seat, was incorporated on March 29, 1823, and as a city on February 15, 1866.

CUMBERLAND COUNTY: created on January 27. 1750 from
part of Lancaster County. Carlisle, the county seat since 1752, was incorporated
April 13. 1782. Shippensburg was the first county seat  (1750 to 1752).

DAUPHIN COUNTY: created on March 4, 1785, from part
Lancastor County. Harrisburg, the county seat, was incorporated on .April 13, 1791, and became a  city on March 19, 1860.
 
DELAWARE COUNTY: created September 26, 1789, from part
of Chester County Media,county seat since 1850, was incorporated  March 11, 1850. Chester, its first county seat. was the county seat of Chester County before
1788 and capital of Pennsylvania, 1681-1682.

ELK COUNTY: created on April 18, 1843, from parts of Jefferson,
Clearfield, and McKean counties. Ridgway, the county seat was incorporated February 15, 1881.

ERIE COUNTY: created on March 12, 1800, from part of
Allegheny County.  It was attached to Crawford County until 1803. Erie, the county seat, was incorporated March 29, 1805, and became a city on April 14, 1851.

FAYETTE. COUNTY: created on September 26, 178S, from part of Westmoreland County, and named for the Lafayette.  Uniontown, the county seat, was originally called Beeson's town and later renamed. It was incorporated on April 4, 1796, and became a city December 19, 1913.

FOREST COUNTY: created on April 11, 1848, from part of Jefferson
County, part of Venango County was added on  October 11,1866. It was administratively attached to Jefferson County until 1857 at which time Marienville became the county seat. Tionesta (the county seat after 1866) was incorporated on February 28, 1856.

FRANKLlN COUNTY: created on September 9, 1784, from part
of Cumberland County. Chambersburg, the county seat, was founded in 1764  was incorporated on March 21, 1803.

FULTON COUNTY: created on April 19, 1851, from part of
Bedford County.  McConnellsburg, the county seat, was incorporated on March 26, 1814.

GREENE COUNTY: created on February 9,  1796, from part of
Washlington County,  Waynesburg, the county seat, was incorporated on January 29, 1816.
 
HUNTINGDON COUNTY: created on September 20, 1787, from
Bedford County. Its county seat Huntingdon was incorporated on March 29, 1796.

INDIANA COUNTY: created on March 30, 1809, from parts of
Westmoreland and Lycoming counties. It was administratively attached to Westmoreland County until 1806. Indiana, the county seat, was incorporated on March 11, 1816.

JEFFERSON COUNTY: created on March 26, 1804, from part of
Lycoming County,  was administratively attached to Westmoreland County until 1806, and then to Indiana County until 1830. BrookviIIe, the county seat, was incorporated April 9, 1834.

JUNIATA COUNTY: created on March 2. 1831. from part of Mifflin
County..   Mifflintown, the county seat, was incorporated on March 6, 1833.

LACKAWANNA COUNTY: created on August l3, 1878, from part
of Luzerne County  Scranton the county seat was  incorporated
in 1856, and became a city on April 21, 1866.

LANCASTER COUNTY: created May 10, 1729 from part of Chester Co. Lancaster, the county seat, was incorporated on May  1, 1742 and became a city on March 20, 1818.

LAWRENCE COUNTY: created on March 20, 1849, from parts of
Beaver and Mercer counties. New Castle, the county seat, was
incorporated  March 25, 1825, and chartered as a city on February 25, 1869.

LEBANON COUNTY: created on February 16, 1819, from part
Dauphin and Lancaster counties. It was first incorporated March 28, 1799, but that was rejected by its citizens.  It was finally chartered  February 20, 1821, and became city in 1885.

LEHIGH COUNTY: created on March 6, l812, from  part of
Northampton County.  Allentown, the county seat, was incorporated as the borough of Northampton on March 18, 1811, renamed Allentown in 1838, and became a city on March 12, 1867.

LUZERNE COUNTY: created on September 25, 1786, from part
Northumberland County. Wilkes Barre,   the county seat
was incorporated on March 17,  1806, and became a city on
May 4, 1871.

LYCOMlNG COUNTY: created on April 1, 1795, from part of
Northumberland County.  Williamsport. the county seat. was incorporated  March 1, 1806, and became a city on January 15, 1866.

McKEAN COUNTY: created on March 26, 1804, from  part
Lycoming County,  was administratively attached to Centre County until 1814, when it was combined with Potter County to elect commissioners jointly, and also attached to Lycoming County for judicial and elective purposes. It became indepententlyorganized in 1826. Smethport, the county seat,  was incorporated Februray 11, 1853.

MERCER COUNTY: created on March 12, 1800, from part of
Allegheny County.  It was administraively
attached to Crawford County until February, 1804, when it was fomally
organized. Mercer, the county seat. was laid out in 1809 and incorporated
March 28, 1814.

MIFFLIN COUNTY: created on September 19, 1789, from parts of
Cumberland and Northumberland counties. Lewistown, the county seat,  incorporated April 11, 1795, but this charter was not accepted,  it was reincorporated on February 6, 1811.

MONROE COUNTY: created on April 1, 1896, from  parts of
Northampton and Pike counties, and named for President James Monroe.
Stroudsburg, the county seat, was incorporated February 6, 1815, and named for Jacob Stroud.

MONTGOMERY COUNTY: created on September 10, 1784, from part
of Philadelphia County.Norristown, the county seat, was incorporated March 31, 1812.

MONTOUR COUNTY: created on May 3, 1850, from part of
Columbia County. Danville, the county seat, and incorporated February 27, 1849. Danville was the county seat of Columbia County from 1813 to 1846.

NORTHAMPTON COUNTY: created on March 11, 1752, from part
of Bucks County, and named for Northamptonshire, England.  Easton, the
county seatwas incorporated  September 23, 1789, and became a city on November 2, 1886.

NORTHUMBERLAND COUNTY: created on 11 March 21, 1772, from
parts of Lancaster, Cumberland, Berks, Bedford, and Northampton
counties. Sunbury,the county seat,  wasincorporated  March 24, 1797,
and became a city in 1921.

PERRY COUNTY: created on March 22, 1820 from part of Cumberland County.  Bloomfield,  the county seat after 1827, was incorporated on March 14, 1831.

PHILADELPHIA COUNTY: one of the of the three original counties
created by William Penn in November, 1682, was chartered as a city on October 25, 1701 and rechartered on March 11, 1789. The county offices were merged with the
city government in 1952.

PIKE COUNTY: created on March 26, 1814, from part of Wayne County.
Milford, the county seat was incorporated on December 25, 1874.

POTTER COUNTY: created on March 26, 1804,  from part
Lycoming County, was administratively attached to Lycoming County until 1814, when it elected commissioners jointly with McKean County.  McKean and Potter
counties were separated in 1824, but Potter remained with McKean
for judicial purposes. It became independent in 1835. Coudersport,
the county seat was incorporated February 7, 1848.

SCHUYLKILL COUNTY: created on March 1, 1811, from parts
of Berks and Northampton counties,  parts of Columbia and Luzerne counties were added March 3, 1818.  Pottsville, county seat after December 1, l851, was incorporated February 19, 1828, and became a city in 1910.  The first county seat was Orwigsburg.

SNYDER COUNTY: created on March 2, 1855, from part of Union Co.
Middleburg, the county seat, was incorporated in 1864.

SOMERSET COUNTY: created on April 17, 1795, from part
Bedord County, and named for Somersetshire, England.  Somerset
the county seat, was  incorporated  March 5, 1804.
 
SULLIVAN COUNTY: created on March 15, 1847, from part
Lycoming County Laporte, the county seat was incorporated during1853.

SUSQUEHANNA COUNTY: created on February 21, 1810, from part
of Luzerne County,  was administratively attached to Luzerne until 1812.  Montrose, the county seat  incorporated March 29, 1824.
 
TIOGA COUNTY: created  March 26, 1804, from part of Lycoming
County.  Wellsboro, the county seat,and incorporated on March 16, 1830.

UNION COUNTY: created  March 22, 1819, from part of North-
umberland County. Lewisburg. thc county seat after 1855, was
 It was incorporated on March 21, 1822.  New Berlin was first
 county seat from 1815 to 1855.

VENANGO COUNTY: created on March 12, 1800, from parts of
Allegheny and Lycoming counties. It  was  administratively attached to  Crawford County until April 1, 1805. Franklin, the county seat was incorporated  on April 14, 1828, and became a city on April 4, 1868.

WARREN COUNTY: created on March 12, 1800, from parts of
Allegheny and Lycoming counties.  It was administratively attached to Crawford County until 1805, and after that to Venango County until 1819, when it was formally organized. Warren,the county seat incorporated Apr 3 1832.

WASHINGTON COUNTY: created on March 28, 1781, from part
Westmoreland County.Washington,  the county seat, was incorporated
February 12, 1810, and chartered as a city in 1924.

WAYNE COUNTY: created on March 21,  1798. Honesdale,
the county seat after 1842, was  incorporated January 28, 1831.  Earlier
county seats were Wilsonville (1799-1802), Milford (1802-1805),
andBethany (1805-1841) .

WESTMORELAND COUNTY: created on. February 26. 1773,
from part of Bedford County. Greensburg, the county seat after 1785, was incorporated February 9, 1799, and became a city in 1928. Hannastown, the original county seat, was burned by British and Indians on July l3, 1782.

WYOMING COUNTY: created on April 4, 1842, from part of
Luzerne County.Tunkhannock, the county seat, was incorporated on August 8,
1841.

YORKCOUNTY: created on August 19, 1749, from part of Lancaster
County. York, the county seat, was  incorporated  September 24, 1787,
Iand became a city January 11, 1887.

This listing is from Pennsylvania History in Outline by Sylvester K. Stevens as Revised and Enlarged by Donald H. Kent ,1964,  Penn Historical and Museum Commission