According to the map of Jefferson County in the book, The Chronology of Jefferson County, by John Long and Peggy T Sinko published 1998, Jefferson County lost to the creation of Belmont County 1,850 square miles on September 7, 1801.  On May 1, 1803 Jefferson County lost land 840 square miles to Columbiana County.  Other counties formed from parts of Jefferson County were; Carroll, Harrison, Mahoning, Summit, Cuyahoga, Lake Geauga, Ashtabula, Trumbull, Portage, and Stark. With boundaries constantly changing, until 1832 when Jefferson County, Ohio took its present shape. 

Jefferson County Boundaries included all of these towns from September 7, 1801 to April 30, 1803

*Denotes those towns currently in Jefferson County, Ohio.

Lexington
Alliance
North Benton
Sebring
Westville
North Benton
Beloit
Damascus
Patmos
New Albany
Calla
Greenford
Woodworth
North Lima
East Lewistown
Washingtonville
New Middletown
New Springfield
Peterburg
Maximo
New Franklin
Homeworth
North Georgetown
Winona
Leetonia
Franklin Square
Middleton
Columbiana
New Waterford
Unity
East Palestine
Paris
Robertsville
Minerva
Bayard
New Alexander
Hanoverton
Kensington
New Garden
Guilford
Lisbon
Signal
Rogers
Elkton
Negley
Clarkson
Oneida
Malvern
Pattersonville
Augusta
Gavers
Millport
Summitville
West Point
Glasgow
Fredericktown
Cannons Mill
Calcutta
New Harrisburg
Carrollton
Mechanicstown
Salineville
Monroeville*
Highlandtown
Wellsville
East Liverpool
Irondale*
Dellroy
Leavittsville
Sherrodsville
Perrysville
Harlem Springs
Amsterdam*
Bergholz*
Hammondsville*
New Somerset*
Port Homer*
Stratton*
Knoxville*
Empire*
New Hagerstown
Kilgore
Wolf Run*
East Springfield*
Fairfield*
Annapolis*
Richmond*
Toronto*
Pekin*
Conotton
Scio
New Rumley
Germano
Wintersville*
Jewett
Cadiz Jct.
Hopedale
East Cadiz
Unionport*
Steubenville*
Bloomingdale*
Mingo Jct.*
New Alexandria*
Cadiz
Unionvale
Robyville
Piney Fork*
York*
Adena*
Smithfield*
Bradley*
Rush Run*
Brilliant*
Moorefield
Piedmont
New Athens
Harrisville
Dillionvale*
Mt Pleasant*
Rayland*
Tiltonsville*