Jacksonville was founded following discovery of gold deposits in 1851–1852. With the creation of Jackson County, it became the county seat, a role which was transferred to nearby Medford in 1927.
Jacksonville was home to the first Chinatown in Oregon, founded by immigrants from San Francisco, California. Evidence of this chapter of history was uncovered early in March 2004 when road work uncovered artifacts dating to the 1850s and 1860s. Construction was halted while archeologists performed four days of rescue excavations. Their findings included broken Chinese bowls and tea cups, handmade bottles, and fragments of opium paraphernalia and Chinese coins.
When the gold deposits were worked out, and the railway bypassed Jacksonville in 1884, the city's economy slowed. This had the unintended benefit of preserving a number of structures, which led to Jacksonville being designated a National Historic District in 1966, covering over 100 buildings. It was cited as a "mid-19th century inland commercial city significant for its magnificent group of surviving unaltered commercial and residential buildings. The city was the principal financial center of southern Oregon until it was bypassed by the railroad."
 2010 census
As of the census of 2010, there were 2,785 people, 1,377 households, and 808 families residing in the city. The population density was 1,473.5 inhabitants per square mile (568.9 /km2). There were 1,548 housing units at an average density of 819.0 per square mile (316.2 /km2). The racial makeup of the city was 95.6% White, 0.4% African American, 0.6% Native American, 0.9% Asian, 0.1% Pacific Islander, 0.6% from other races, and 1.9% from two or more races. Hispanic or Latino of any race were 2.9% of the population.
There were 1,377 households out of which 18.3% had children under the age of 18 living with them, 50.5% were married couples living together, 6.1% had a female householder with no husband present, 2.0% had a male householder with no wife present, and 41.3% were non-families. 36.9% of all households were made up of individuals and 21.1% had someone living alone who was 65 years of age or older. The average household size was 2.02 and the average family size was 2.62.
The median age in the city was 54.9 years. 15.9% of residents were under the age of 18; 4.3% were between the ages of 18 and 24; 14.8% were from 25 to 44; 35.1% were from 45 to 64; and 30% were 65 years of age or older. The gender makeup of the city was 46.2% male and 53.8% female.