The first boundaries of Hastings County were established 1792 by Lieutenant-Governor John Graves Simcoe. The Bay of Quinte was the southern boundary, Lennox County was the eastern boundary, and the western boundary ran from the Trent River to the Ottawa River, in a triangular shape.
The County consisted of Sidney, Thurlow, Rawdon, Huntingdon and Hungerford townships, as well as the Mohawk Tract. The area was named for Francis Rawdon-Hastings. Three new townships of Elzevir, Madoc and Marmora were created in 1821.
Agriculture was the most important industry in Hastings County, but by 1822 (when the Marmora Iron Works was approaching its peak production) mining was playing an increasingly more important role in the area's economy.
From 1839 until 1849, Hastings County was renamed Victoria District after Queen Victoria. In 1856 the first railroad train arrived in Belleville, and this, along with more good gravel roads being built, attracted more settlers to Hastings County starting around 1880.