After 1840 the agricultural frontier reached past Missouri. The opening of land was due in large part to French and Scots-Irish trappers who explored and mapped rivers and mountain passes which made possible the settlement in the 1840s and on.
One group who moved West together was the Mormons. By 1843, several thousand Americans had taken the Oregon Trail into the Willamette Valley. About 800 Americans had taken the more southern route to California.
Cincinatti had approximatley 75,000 people which is more than any other city west of the Appalachians.