[8] Jefferson County was established on June 11, 1792, by William Blount, Governor of the Southwest Territory.

[10] A railroad bridge at Strawberry Plains was among those targeted by the East Tennessee bridge-burning conspiracy in November 1861.

[11] This led to internal conflict in the area throughout the war, with men from the county enlisting in both of the rival armies.

On October 2, 2013, on I-40 in Jefferson County near the I-40 and I-81 split, a multi-vehicle collision involving a church bus, a tractor-trailer, and a SUV occurred at mile marker 423.

[12] Tennessee Highway Patrol officials discovered that the church bus had blown a tire, leading it to merge into oncoming traffic, clipping the SUV and colliding with the semi-truck, causing it to burst into flames.

As of the 2020 United States census, there were 54,683 people, 20,154 households, and 13,998 families residing in the county.

However, the last statistic is somewhat misleading because of female longevity, and if adults 18-65 were considered, the numbers would be very close to equal.