First Spanish Explorers 

According to the website onlyinark.com, "The Spanish were the first explorers to set foot in Arkansas. Hernando de Soto arrived in Arkansas with his expedition in 1541. He crossed the Mississippi River into Arkansas on June 28, 1541, and spent the next year roaming the state. De Soto’s expedition was a key point in Arkansas history. He was not only the first European contact the Indigenous populations experienced, but his group of explorers unintentionally brought numerous diseases with them. De Soto described large communities of people living in towns who had the ability to raise an army of thousands if needed. When the French arrived over 100 years later, these populations had been nearly wiped out by diseases like measles, smallpox, influenza and other respiratory infections."[2]

French Explorers

According to encyclopediaofarkansas.net, 

"In 1673, Father Jacques Marquette, a Jesuit missionary, and Louis Joliet (or Jolliet), a fur trader, undertook an expedition to explore the unsettled territory in North America from the Great Lakes region to the Gulf of Mexico for the colonial power of France. Leaving with several men in two bark canoes, Marquette and Joliet entered the Mississippi River and arrived in present-day Arkansas in June 1673. They were considered the first Europeans to come into contact with the Indians of east Arkansas since Hernando de Soto’s expedition in the 1540s. The goal given Marquette, Joliet, and their men was to document, for French and Canadian officials, an area that had been largely unknown until the late seventeenth century."

"The importance of the expedition of Marquette and Joliet includes the realization of French dreams of an all-water route between the Great Lakes region and the Gulf of Mexico. French officials—based on reports from Marquette, Joliet, and Arkansas’s Quapaw Indians— could begin to build forts to along the river, place a barrier between themselves and the English colonies, and expand the Catholic faith. More importantly, the information gained by the explorers paved the way for the expeditions of other Frenchmen, including René-Robert Cavelier, Sieur de La Salle, in 1682 and Henri de Tonti, who came to Arkansas and established Arkansas Post (Arkansas County) in 1686, the first European settlement in the Lower Mississippi River Valley. Marquette and Joliet also established that American Indians in the lower Mississippi River Valley, especially those in Arkansas, could become valuable allies to the French."[5]