The Pennsylvania State Library has an excellent collection of maps and county atlases for almost all counties. Most of these atlases were published from 1850 to 1880. You can write to the library to order a map for a particular town or county.
A helpful guide to the holdings at the State Archives is Martha L. Simonetti, comp., Donald H. Kent and Harry E. Whipkey, eds., Descriptive List of the Map Collection in the Pennsylvania State Archives (Harrisburg, PA; Pennsylvania Historical and Museum Commission, 1976; FHL book 974.8 E73p; film 1321380 item 2). The university libraries in Pennsylvania also have map collections.
For a listing of topographical maps see United States, Geological Survey, Pennsylvania: Index to Topographic and Other Map Coverage (Reston, Virginia: The Survey, [1983?]; FHL book 974.8 A1 no. 665).
The Family History Library has many maps of Pennsylvania. Atlases for the years 1790, 1810, 1823, 1838, 1857, 1862, 1878, 1884, and 1917 are on FHL film 2083. Another useful atlas is H.F. Walling and O.W. Gray, Historical Topographical Atlas of the State of Pennsylvania(1872; reprint, Knightstown, Indiana: Bookmark, 1977; FHL book Q 974.8 E3w).
An excellent atlas, comprehensive in detail, is Atlas of Pennsylvania (Philadelphia, PA: Temple University, 1989; FHL book 974.8 E7ap). The historical portion of this work is published separately as Edward K. Muller, ed., A Concise Historical Atlas of Pennsylvania (Philadelphia, PA: Temple University Press, 1989; FHL book Q 974.8 E7apa).
Maps showing county boundaries include:
Long, John H., ed. Pennsylvania: Atlas of Historical County Boundaries. (New York, NY: Charles Scribner's Sons, Simon and Schuster Macmillan, 1996. (FHL book 974.8 E3p.)
Long, John H., ed. Historical Atlas and Chronology of County Boundaries, 1788-1980. Vol. 1, Delaware, Maryland, New Jersey, Pennsylvania. Boston, Mass.: G.K. Hall, 1984. (FHL 973 E7hL v. 1; fiche 6051426.)
County Historical Maps. Harrisburg, PA: Archives Publishing of Pennsylvania, [19--]. (FHL Q book 974.8 E3ch.) Includes historical annotations for 28 counties.
To locate Philadelphia wards and townships from 1711 to 1965, see John Daly and Allen Weinberg, Genealogy of Philadelphia County Subdivisions, 2nd ed. (Philadelphia, PA: Department of Records, 1966; FHL 974.811 E3w; fiche 6046613).
City ward maps can be helpful when using census records. See Ward Maps of United States Cities: Microfilm Reproduction of 232 Maps Described in Ward Maps of United States Cities. Washington, D. C.: Library of Congress, [1975?]. (FHL film 1377700; on 320 fiche beginning with 6016554.) These include:
- Allegheny, 1867-78 (FHL fiche 6016561-66)
- Philadelphia, 1802-98 (FHL fiche 6016721-36)
- Pittsburgh, 1855-98 (FHL fiche 6016737-43)
There are also Historical Pennsylvania Maps available online. Try using a search engine with the terms "Historical Pennsylvania Maps".
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html