County Named, 1806. For Meriwether Lewis of Lewis and Clark expedition, sent out by President Jefferson to explore the northwest, 1804-05. Followed the Missouri River to source, crossed mountains, then Columbia River to Pacific. Lewis born Va., 1774. US army, 1795; captain, 1800. Private Secretary to Jefferson, 1801-03. Terr. Gov. of Louisiana, 1807-09. Died, 1809, buried in Tennessee.