Joseph Nicolas Nicollet (July 24, 1786 – September 11, 1843), also known as Jean-Nicolas Nicollet, was a French geographer and  mathematician known for mapping the Upper Mississippi River basin during the 1830s.

Nicollet was born in Cluses, Savoy, France. He was very bright, showing an interest in mathematics and astronomy, and becoming a math teacher at the age of 19. Starting in 1817, he worked at the Paris Observatory with the mathematician Pierre-Simon Laplace. Afterward, he worked as a mathematics professor at the Collège Louis-le-Grand during the 1820s.

Following financial difficulties in France, Nicollet emigrated to the United States in 1832. First living in New Orleans, Louisiana, he later moved up the Mississippi River to St. Louis, Missouri. Nicollet led three expeditions exploring the Upper Mississippi, mostly in the area that is now Minnesota, but parts of North and South Dakota as well. The first took place in 1836–37 and was largely funded by St. Louis's wealthy Choteau family. In it, Nicollet explored the Mississippi to its source of Lake Itasca and the nearby Mississippi tributary, the St. Croix River. Following acceptance of a position with the United States Army Corps of Topographical Engineers in 1838, Nicollet led a surveying mission from Fort Snelling to the Pipestone region in southwestern Minnesota and southeastern South Dakota in 1838, and led another mission in 1839 to further explore the region between the Mississippi River and the Missouri River. In these latter expeditions, he had assistance from John C. Frémont and the Jesuit Missionary Pierre-Jean De Smet. De Smet used skills learned from Nicollet to make his own maps of the Missouri River basin.

After the expeditions, Nicollet left the Minnesota area to go to Washington, D.C. He worked on consolidating the information collected during the expeditions and fully intended to return to the area, but failing health led to his death in Washington in 1843. Later that year, a book containing much of his work, Map of the Hydrographical Basin of the Upper Mississippi, was published. The maps in the book were highly accurate and covered a region more than half the size of Europe.

Nicollet's name is applied to several places in the region he explored, including Nicollet Island, Nicollet Avenue in Minneapolis, Nicollet County and the city of Nicollet, all located in Minnesota.