The meaning of Alachua is suggested by a passage in the journal of Lieutenant Diego Peña, who on his expedition to Apalachee and Apalachicola in 1716, traversed the region, and of the area between the Ichetucknee and Suwannee Rivers in southern Suwannee County remarks:
The 21st day I left the said site (adjacent to the Itchtucknee River) and camped at a place they call Aquilachua this day I marched five leagues. In this day's march no creeks were encountered but there are good springs of water, and the first (is) named Usichua, (and) the other Usiparachua, and another Afanochua.|20px|20px
That the springs without effluent streams were sinkholes is consistent with the area, which has many. The names of these watering places all possess the terminator chua, which suggests that chua is the Timucuan name for sinkhole. This inference is not inconsistent with the general opinion of residents of the county, that the name Alachua means sinkhole.
Alachua County proper was created in 1824. The original county seat was Newnansville located near the current site of the city of Alachua. In 1853, the new railroad from Fernandina to Cedar Key bypassed Newnansville, and Gainesville, a new town that was located on the railroad, began to draw business and residents away from Newnansville. Gainesville became the county seat the following year.
There were 87,509 households out of which 25.20% had children under the age of 18 living with them, 38.80% were married couples living together, 12.30% had a female householder with no husband present, and 45.40% were non-families. 29.10% of all households were made up of individuals and 6.40% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.94.
In the county the population was spread out with 20.20% under the age of 18, 23.20% from 18 to 24, 27.70% from 25 to 44, 19.30% from 45 to 64, and 9.60% who were 65 years of age or older. The median age was 29 years. For every 100 females there were 95.40 males. For every 100 females age 18 and over, there were 93.20 males.
The median income for a household in the county was $31,426, and the median income for a family was $46,587. Males had a median income of $31,971 versus $26,059 for females. The per capita income for the county was $18,465. About 12.20% of families and 22.80% of the population were below the poverty line, including 19.40% of those under age 18 and 9.70% of those age 65 or over.