According to the United States Census Bureau, the city has a total area of 7.2 square miles (18.7 km²), of which, 7.1 square miles (18.3 km²) of it is land and 0.1 square miles (0.3 km²) of it (1.80%) is water.
There were 380 households out of which 30.3% had children under the age of 18 living with them, 62.1% were married couples living together, 10.8% had a female householder with no husband present, and 23.9% were non-families. 22.6% of all households were made up of individuals and 11.1% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 2.92.
In the city the population was spread out with 23.8% under the age of 18, 8.9% from 18 to 24, 27.4% from 25 to 44, 25.8% from 45 to 64, and 14.2% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 96.7 males. For every 100 females age 18 and over, there were 88.3 males.
The median income for a household in the city was $31,042, and the median income for a family was $40,000. Males had a median income of $27,222 versus $23,393 for females. The per capita income for the city was $13,914. About 11.1% of families and 8.9% of the population were below the poverty line, including 12.6% of those under age 18 and 11.8% of those age 65 or over.
For thousands of years, Native Americans hunted and camped along the banks of the Little Tennessee River. The Icehouse Bottom site, located a few miles southwest of Greenback, is believed to have been inhabited as early as 9,000 years ago, making it one of the oldest known habitation sites in Tennessee. By the time Euro-American explorers and settlers arrived in the area in the 1700s, the villages of the Overhill Cherokee dominated the river, stretching from the village of Tallassee (near modern Calderwood) to Mialoquo (near the modern US-411 bridge). In the late 1790s, the Tellico Blockhouse was expanded to help facilitate trade between the Overhill towns and Knoxville, which was a few miles downstream to the north. As there were no major bridges spanning the Little Tennessee at the time, ferries became an important means of getting across the river. Among the earliest and most important of these ferries was the one at Morganton, located a few miles west of what is now Greenback.
Morganton Ferry— initially called "Wear's Ferry"— was established in the late 1700s, and had grown into a small community known as "Portville" by 1810. It was officially chartered as "Morganton" in 1813, named after Revolutionary War veteran and local merchant, Gideon Morgan. Around this time, the Tellico Agency was moved from the Tellico Blockhouse to Fort Southwest Point (now Kingston), expanding Southwest Point's importance and influence. In response, a road quickly developed between Maryville and Southwest Point. Since the road crossed the Little Tennessee at the Morganton Ferry, the road became known to Blount Countians as Morganton Road. The first commercial structure in what is now Greenback was probably the Norwood Inn, which was a stopover for merchants and farmers traveling from Maryville to Morganton. Traffic along Morganton Road increased steadily until the American Civil War, when intrastate commerce declined.
In the years leading up the Civil War, a cave in the Morganton and Greenback area is believed to have been a stop on the Underground Railroad, perhaps reflecting the area's ties to abolitionist-heavy Blount County.
In 1859, entrepreneur Jesse Kerr established a hotel and health resort at the mineral-rich Sulphur Springs near the base of Chilhowee Mountain several miles southeast of Morganton (the resort was located near the modern junction of US-129 and TN-336). The resort was connected to Morganton Road via a stagecoach road which roughly paralleled what is now Highway 95.
In 1876, Lorenzo Thompson established Thompson's Stand, a general store situated at the junction of the Sulphur Springs coach road and Morganton Road. Hoping to draw traffic to his store, Thompson submitted a request to establish a post office at Thompson's Stand in 1882. The Postal Service rejected his initial name for the town of Thompson Station, as well as subsequent submissions Pine Grove and Alleghany Station, all of which were already taken. The town finally settled on the name "Greenback," which was inspired by a local politician and member of the Greenback Party named Jonathan Tipton.
In 1885, Indiana businessman Nathan McCoy purchased the Sulphur Springs resort with plans to expand it. In the summer of 1886, the resort reopened with a newly-constructed 3-story, 60-room hotel under the new name of Alleghany Springs. The resort was instrumental in luring the L&N Railroad to the head of its coach road at Greenback, where it had established Alleghany Station for its guests making the trek from Knoxville.
With the arrival of passenger train service from Knoxville, Greenback grew quickly. In the early 1890s, the young town had its own grist mill, blacksmith, physician, shoemaker, and general store. In the early 1900s, the L&N Railroad constructed a second line through the town, opening a depot in 1914. By 1920, the town had its own bank and several industries, including the Greenback Motor Company. Several fires throughout the 1920s and the Great Depression, however, halted the town's rapid growth.
Greenback was officially incorporated in 1957, with Glenn McTeer as its first mayor. A community center— built by the town's residents with no outside help or outside funding— was completed in 1978. It now houses a library, the city hall, and recreational facilities.