Created on March 12, 1800 from parts of Allegheny and Lycoming Counties. Its name comes from the Indian name for French Creek. It was attached to Crawford County until April 1, 1805. Franklin, the county seat, was laid out in 1795 at Fort Franklin, which had been built in 1787 by United States troops. Both were named for Benjamin Franklin. Franklin was incorporated as a borough on April 14, 1828 and as a city on April 4, 1868.

     What is now Franklin was the site of a French fort (1754–1759), a British Army fort (1760–1763), and the U S. Army’s Fort Franklin (1787). The area was purchased from Indians at Ft Stanwix in 1784 (the “Last Purchase”). The land west of the Allegheny River was Donation Land intended for Revolutionary army veterans. The Holland Land Company’s titles were disputed by “actual settlers,” and these cases dissuaded many from moving in to establish farms. Before the 1859 oil boom, pig iron was main the main export product. When Colonel Drake struck oil, boomtowns arose overnight. Oil City is one that survived, but Pithole City and others did not. Oil City’s oil exchange was a major national economic player, but it closed in 1909. Refineries and oil equipment manufacture continued to flourish, and railroads rushed to the oil areas. Bad floods occurred in 1865, 1883, 1892, 1913, 1926, 1936, 1981, and 1982. A dam that collapsed above Titusville wiped out much of Oil City in 1892, but it was rebuilt. Peak population was achieved in 1950: 65,328. Today the refineries are gone, though some oil well tools are still made. The energy crises of the 1980s brought renewed attempts to produce more oil, although major amounts were not forthcoming. Venango is a minor bituminous producer. Farms cover 15 percent of the county.