Yes it is. Another of the History Mysteries of Florida is that one time Florida actually did go all the way to the Mississippi River. In fact, when the British owned Florida it was actually two colonies - West Florida and East Florida.
Upon signing the Treaty of Paris in 1763, to end the Seven Years War, Spain lost Florida to the British. The British divided the new territory into two separate colonies: West Florida with its capital at the former Spanish settlement of Pensacola and East Florida, with its capital in St. Augustine. When the British acquired these two new colonies they added them to the other 13 colonies they already had in the new world.
During the twenty year British Period (1763-1783), Florida went through significant change in ownership and in settlement that would have a profound effect on defining its future boundaries.
The royal proclamation of 1763 defined the boundaries of West Florida to be the Gulf of Mexico to the south, Lakes Pontchartrain and the Mississippi River to the west, the thirty-first parallel to the north, and the Chattahoochee and Apalachicola Rivers to the east. So yes, West Florida, when it was owned by the Spanish and the British, went all the way to the Mississippi River. But in 1764 Florida grew even larger.
In 1764, Colonial Governor Johnstone moved the northern border to a line drawn due east from where the Yazoo River meets the Mississippi River. Johnstone extended the border for political and economic reasons, to include a much larger settlement along the Mississippi River and more fertile land. Much of this northern land was occupied by the Choctaw, Creek, and Chickasaw Indians. You have to realize that both West Florida and East Florida were just English colony (just like the original 13 colonies) for 20 years, before and during the Revolutionary War.
For nearly 20 years, West Florida was actually larger than East Florida and took in much of what would later become Mississippi and Alabama. The picture above is at Mile Marker 107.9 on the Natchez Trace (107.9 miles north of Natchez, Mississippi) and shows very clearly the size of West Florida during that period (the red area).
West Florida was invited to send delegates to the First Continental Congress. This meeting of the colonies, which was leading up to the revolutionary war, was convened in Philadelphia in 1774. They met to present colonial grievances against the British Parliament to King George III. However West Florida, along with several other colonies including East Florida, declined the invitation.
Florida did not join its fellow thirteen English colonies in the revolution but remained loyal to England. Its previously sparse population swelled overnight as Tories escaped into loyalist Florida, mostly settling in St. Augustine, in East Florida. Florida was not one of the English colonies that became the United States when they were officially recognized as independent in 1783. Florida remained under British control.
So yes, West Florida went all the way to the Mississippi River, but it also at one time went way up into what is today: the middle of the state of Mississippi and Alabama. But of course, that all changed when Spain re-acquired West Florida and East Florida back from the British at the close of the Revolutionary War. Then, in 1819, Spain agreed to cede Florida to the United States, but that is another story.
H. C. “Hank” Klein is a Destin historian who visits often and lives in North Little Rock, Arkansas with his wife (the former Muriel Marler of Destin). Klein recently published a historic book about Destin's pioneer settlers. DESTIN Pioneer Settlers...A Land History of Destin, Florida from 1819-1940 can be obtained from Amazon.com, Tony Mennillo of Arturo Studios at 850/585-2909, Dewey Destin's Restaurants, in Destin, the Magnolia Grill in Fort Walton Beach, or Bayou Books in Niceville. Klein can be contacted at klein@aristotle.net.