Benton County and Bentonville are named in honor of Thomas Hart Benton, a U.S. Senator from Missouri, who played a key role in persuading Congress to admit Arkansas to the Union on September 30, 1836, as the 25th state. The county was organized in 1836. Benton County is 886 square miles with a perimeter of 142.25 miles. The topography is gentle rolling hills (Ozark Mountains). The average annual rainfall is 40 to 45 inches. The U.S. Census Bureau reports a population of 153,406 in Benton County in 2000, with an estimated population of 172,003 in 2003 (a 12.1% increase).  Bentonville is the county seat and had an estimated population of 26,397 in 2003, according to the U.S. Census Bureau. There are 17 incorporated cities and towns and  6 unincorporated towns in the County.