I think that you can take this in several ways.  The first way I would address it is to note that Neoclassicism in Europe was prevalent in the late 1700s to the mid 1800s.  In America, it emerged in Revolutionary literature, and life after the Revolution.  It can be seen in America literature that develops in the formative period of the Constitutional Convention and settles in during the period of Jefferson and afterwards, with American expansion.  The time it stops would be around the Age of Reform, about the mid 1800s, as American industry began to develop and the Transcendental movement coincided with it.  Just as Romanticism overtook Neoclassicism in Europe, it was overtaken by Transcendentalism and the Age of Reform in America.