LaPorte County was formed in 1832. La porte means "the door" or "the port" in French. French travelers or explorers so named the area after discovering a natural opening in the dense forests that used to exist in this region, providing a gateway to lands further west.
Before white settlement, all of the land that forms modern-day LaPorte County, and adjacent Starke County to the south belonged to the Potawatomi Indian nation. These Indians were forcibly removed to Kansas by the United States government in 1838, and many died on what survivors called the Trail of Death.
LaPorte County's initial White American settlers were Yankee immigrants, that is to say they were from New England or were from upstate New York and had parents who were from New England, and were descended from the English Puritans who settled New England in the colonial era. They were part of a wave of New England settlers moving west into what was then the Northwest Territory after the completion of the Erie Canal. The original White settlers in LaPorte County specifically hailed from the Massachusetts towns of Granville, Boston, Bridgewater, West Bridgewater, Andover, Nantucket Island and Hampshire County; the Connecticut towns of Colchester, Wethersfield, Granby and New Haven; the New Hampshire towns of Bradford, Amherst and Goffstown; the Vermont villages of Dorset, Albany and Fairfax; many also came from Orange County, Vermont, Caledonia County, Vermont and Penobscot County, Maine. They were mainly members of the Congregational Church, but as a result of the Second Great Awakening many became Baptists and many also converted to Pentecostalism and Methodism. When they arrived in what is now LaPorte County, there was nothing but virgin forest and wild prairie, the New England settlers cleared roads, built farms, constructed churches, erected government buildings, and established post routes. As a result of this migration, LaPorte County was culturally continuous with early New England culture for many years.
When the county was initially proposed and organized, its boundaries did not extend as far south or east as they do today. A section of land north of the Kankakee River originally belonged to Starke County. However, residents living in that area had difficulty crossing the river in order to reach the rest of the county. It was necessary to travel some distance east to Lemon's bridge, before making the journey south. Effectively isolated from the rest of Starke County, these residents asked that their land be annexed to LaPorte County, which was completed on January 28, 1842. Thereafter, the Kankakee River formed the southern boundary of the county. Finally, on January 10, 1850, some twenty sections of land were annexed from St. Joseph County to the east, giving LaPorte County the boundaries that essentially exist to this day.
Whether the correct spelling of the city and county is "La Porte" or "LaPorte" is disputed, although state law refers to "LaPorte County."
LaPorte County is also famous for being the scene of the Belle Gunness serial murders. She lived on a farm on the outskirts of LaPorte County.