John Charles Frémont was born in Savannah, Georgia in 1813. Though poor, through the efforts of a family friend, John Charles was prepared for and entered Charleston College at the age of 16. In one year he had advanced to the Junior Class, and though he showed great promise in languages, science, and mathematics, a few weeks before graduating he was expelled for non-attendance.
He early worked as a schoolteacher, teacher of mathematics, and surveyor. Attracting the attention of Joel Poinsett (former Senator, Ambassador to Mexico, and later Secretary of War) Frémont was commissioned as Professor of Mathematics in the Navy. The appointment convinced Charleston College to then confer upon him the degrees of Bachelor and Master of Arts. He was assigned to the Frigate Independence, where he taught mathematics to midshipmen--there not yet being a Naval Academy at that time.
In 1837, at the age of 24, he was appointed a civil engineer in the Army Topographical Corps of Engineers by President Jackson. A number of government and railroad surveys followed. In 1838 was commissioned as Second Lieutenant of Topographical Engineers.
In 1838 and 1839 he was assigned to a survey of the area between the upper Missouri and Mississippi Rivers under Joseph Nicolas Nicholet, an eminent French astronomer and mathematician. He had also become attracted to the 15 year old daughter of the powerful Missouri Senator Thomas Hart Benton. The attraction was mutual, but Jessie Benton's age, and Frémont's birth and Army career, made him unsuitable as a suitor. The Nicholet survey, and an 1841 survey of the Des Moines River, kept Frémont conveniently apart from Jesse. But on his return the two became secretly married.
Senator Benton was furious over the marriage, but soon became reconciled to the union, and thereafter used his influence at every opportunity to promote Frémont's career. This came soon, in 1842. Because of ill health, Nicholet was unable to conduct a mapping expedition of the Oregon Trail to the Rockies through the South Pass. The command fell to Frémont. Now known as Frémont's First Expedition, the results were a great success, and the report written in a narrative form by Frémont with the assistance of Jessie, was published by Congress in 1843 and appeared in all major newspapers. The Report made Frémont known and also introduced Christopher "Kit Carson" to the American public.
Frémont's Second Expedition was an even greater success. It included many men from his First Expedition, including cartographer Charles Preuss, and Kit Carson. Dividing his men, he sent most of the expedition along his previous route under mountain man and trapper Thomas "Broken Hand" Fitzpatrick. Frémont traveled a new route to include the first mapping and exploration of the Great Salt Lake. Reuniting the party at Fort Hall, he then continued on to Fort Vancouver, tying his survey in to the recently completed Wilkes Coastal Survey.
The Expedition then moved south through what is now central Oregon and western Nevada arriving a what Frémont named Pyramid Lake. It was mid winter, and being low on supplies, he decided to cross the Sierra Nevada to Sutter's Fort on the Sacramento River. This turned into a monumental effort, but was ultimately accomplished. Every detail of this mountain crossing is covered in The Crossing described on this site.
Traveling south through the Sacramento and San Joaquin Valleys, the Expedition joined the old Spanish Trail, from which it later turned north and returned to Missouri. The Report of this expedition, after an initial printing of 20,000 copies by the Senate and the House of Representatives, was published world wide. The map of 1845 produced and published with the report was the first accurate map of the region west of the Rocky Mountains, and was the basis of later maps of the area for many years. Frémont was now a national hero, as was Kit Carson. Second Lieutenant John Charles Frémont, now popularly known as "The Pathfinder", was awarded a double brevet in rank.
The next year, Captain John Charles Frémont left Missouri on his Third Expedition. The goal of this expedition is less clear. The United States was on the verge of war with Mexico over the annexation of Texas. It was feared that in the event of war, California, removed from Mexico and beyond Mexico's ability to protect, might fall under the protection of England or France. Mexico owed England a large war debt from their own war of independence. That and the unsettled joint occupation of the Oregon Territory by the United States and England seemed to require a military presence in California.