Origin and history of Monroe

the surname (also Munroe, etc.) is said to be ultimately from the River Roe in Derry, Ireland. James Monroe (1758-1831), the fifth U.S. president, was in office from 1817 to 1825. The Monroe Doctrine (so called from 1848) is a reference to the principles of policy contained in his message to Congress on Dec. 2, 1823. Monrovia, the capital of Liberia, also was named for him at its founding in 1822 by the American Colonization Society.

In terms of national psychology, the Monroe Doctrine marked the moment when Americans no longer faced eastward across the Atlantic and turned to face westward across the continent. [Daniel Walker Howe, "What Hath God Wrought"]