The place name Kealia means salt encrustation or salt land, implying that the area was a source of salt in traditional times. During the pre-contact period (prior to 1778), Kealia was home to a large settled population of farmers and fishermen, who took advantage of the abundant natural resources and abundant rainfall inland and upland from the coasts. Kealia Beach, directly across the road from Kealanani, was no doubt extensively used for agriculture during pre-Contact times.

Native Hawaiians built impressive irrigation systems in eastern Kauai to transport stream water to agricultural fields during traditional times. These ancient agricultural resources, including an extensive ditch irrigation system in Kapaa, were still functioning as late as the early 20th century.

Only a few stories have survived concerning early events at Kealia. One involves the mythological Hiaka, the sister of Pele the fire goddess. When Hiaka was sent to fetch Pele's lover at Haena, she passed through Kealia, where she instantly restored to health a sick woman whom none of the local kahuna (chiefs) had been able to cure.

One indication of the political importance of the area is the number of heiau (religious shrines). In the 1880s nine were listed between Kealia and Kapaa. Unfortunately, the location of most of these structures has been lost.

The earliest written references to the Kealanani area date from the early 1830s when missionaries reported a population of 283 living in Kealia. At that time, several land areas (kuleana) were used for growing taro.

Kealia has a long history of agriculture beginning with this taro cultivation. In the mid-1800s cotton was planted, and there are records of a dairy dating back to 1860. In the 1930s rice was planted. Pineapple was also grown in the area, but the dominant crop from the latter 19th century to the late 20th century was sugar cane. The Kealia Sugar Plantation was in operation from 1869 to 1885. Colonel Zephaniah Spalding and his father, Civil War veteran Captain James Makee, purchased the Krull cattle ranch and dairy farm in Kealia/Kapaa in 1876. Spalding formed a hui (a group of individual investors) who financed the creation of the Makee Sugar Company, in which King David Kalakaua had a 25 percent investment.

Kealia Plantation was established to cultivate and process sugar at mills in Kapaa and Kealia. In 1916, Colonel Spalding sold his holdings to the Lihue Plantation Company. The Kealia mill was dismantled in 1934 and transported by rail to Lihue, where today it still sits beside Highway 50.