What year did the Mormons make their first trek?

In the winter of 1847, the Mormons first left Illinois. They traveled as far as Omaha, Nebraska where they build a temporary settlement to wait for spring to come. When spring came, they made their preparations and continued their journey to the Great Salt Lake Valley. In the years that followed many more Mormons would make the same trek.

Technically the "Mormons," or followers of Joseph Smith, made their first trek in January-February 1831 from upstate New York to Kirtland, Ohio.