This work contains the 1783 tax lists for Washington County which were lost until 1982 when a duplicate set of the records was found in Harrisburg quite by chance; these records will be a boon to researchers interested in southwestern Pennsylvania. Tax lists form a very important adjunct to census records because they were normally compiled every year, indicate place of residence, show ownership of real estate and livestock, and can frequently be used to determine when a man turned twenty-one years of age. The Washington County of 1783 included all of south-western Pennsylvania west of the Monongahela River and south of the Ohio River, i.e., it included all of present-day Washington and Greene Counties as well as parts of Allegheny and Beaver Counties. The tax records have been supplemented by a restructured edition of the 1790 Federal Census of Washington County, which has been rearranged by townships, a rearrangement that was made possible by the discovery of the tax lists. This work contains several helpful maps which show former and current county boundaries.