Question: The biggest tributary of the Mississippi runs through what Indiana county?

full_context: Document 1: Indiana: Indiana is a U.S. state located in the midwestern and Great Lakes regions of North America. Indiana is the 38th largest by area and the 17th most populous of the 50 United States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th U.S. state on December 11, 1816. Indiana borders Lake Michigan to the northwest, Michigan to the north, Ohio to the east, Kentucky to the south and southeast, and Illinois to the west.
Document 2: Clarksville, Indiana: Clarksville is a town in Clark County, Indiana, United States, along the Ohio River and is a part of the Louisville Metropolitan area. The population was 21,724 at the 2010 census. The town was founded in 1783 by early resident George Rogers Clark at the only seasonal rapids on the entire Ohio River, it is the oldest American town in the former Northwest Territory. The town is home to the Colgate clock, one of the largest clocks in the world and the Falls of the Ohio State Park, home to the world's largest exposed Devonian period fossil bed.
Document 3: Missouri River: The Missouri River is the longest river in North America. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2341 mi before entering the Mississippi River north of St. Louis, Missouri. The river takes drainage from a sparsely populated, semi-arid watershed of more than half a million square miles (1,300,000 km), which includes parts of ten U.S. states and two Canadian provinces. When combined with the lower Mississippi River, it forms the world's fourth longest river system.
Document 4: Snake River: The Snake River is a major river of the greater Pacific Northwest in the United States. At 1078 mi long, it is the largest tributary of the Columbia River, the largest North American river that empties into the Pacific Ocean. Rising in western Wyoming, the river flows through the Snake River Plain of southern Idaho, then through the rugged Hells Canyon area via northeastern Oregon and the rolling Palouse Hills, to reach its mouth near the Washington Tri-Cities area, where it enters the Columbia. Its drainage basin encompasses parts of six U.S. states, and its average discharge is over 54000 cuft/s .
Document 5: Ohio River: The Ohio River, which streams westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi (Ohio at Cairo: 281,500 cu ft/s (7,960 m/s); Mississippi at Thebes: 208,200 cu ft/s (5,897 m/s)) and, thus, is hydrologically the main stream of the whole river system.
Document 6: Whitewater River (Great Miami River): The Whitewater River is a 101 mi southerly flowing right tributary of the Great Miami River in southeastern Indiana and southwestern Ohio in the United States. It is formed by the confluence of two forks, the West Fork and East Fork. The name is a misnomer, as there is no true white water on the river. However, there are many rapids due to the steep gradient present - the river falls an average of 6 ft/mile . The gradient rendered upstream navigation impossible, and in the mid-nineteenth century resulted in the construction of the Whitewater Canal paralleling the river from north of Connersville, Indiana, to the Ohio River.
Document 7: Cumberland River: The Cumberland River is a major waterway of the Southern United States. The 688 mi river drains almost 18000 mi2 of southern Kentucky and north-central Tennessee. The river flows generally west from a source in the Appalachian Mountains to its confluence with the Ohio River near Paducah, Kentucky, and the mouth of the Tennessee River. Major tributaries include the Obey, Caney Fork, Stones, and Red rivers.
Document 8: Columbia River: The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada. It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is 1243 mi long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province. The fourth-largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific.
Document 9: River Bend (Illinois): The River Bend is a small region in western central Illinois and Southern Illinois that comprises parts of three counties: Madison, Calhoun, and Jersey. The name comes from a section of Mississippi River that flows roughly west to east instead of the usual north to south, causing a bend in the river. In this area, two other major rivers, the Missouri and the Illinois join the Mississippi River. This section of the Mississippi River is known as the Alton Lake
Document 10: Wheeler, Indiana: Wheeler is an unincorporated census-designated place (CDP) in northern Union Township, Porter County, in the U.S. state of Indiana. It lies along State Road 130, northwest of the city of Valparaiso, the county seat of Porter County. Its elevation is 666 feet (203 m). Although Wheeler is unincorporated, it has a post office, with the ZIP code of 46393. The population of Wheeler was 443 at the 2010 census. Wheeler has seen small growth, although its unincorporated, but the estimated population of Wheeler at the 2014 estimate was 452. The 2014 population area estimate of and around Wheeler was 1,685. Wheeler is served by the Union Township School Corporation, which includes Wheeler High School, Union Township Middle School, and two elementary schools. Wheeler today is still part of Union Township and has remained as the largest community in the township by population.
Document 11: Sargents, Ohio: Sargents is an unincorporated community in Pike County, Ohio, United States. The closest highway is U.S. Route 23, the main street is Wakefield Mound Road, and the closest town is Piketon. Sargents is named after the Sargent brothers who came from Maryland in the 1790s. They worked to start a station for liberated slaves in Ohio, which later became later part of the underground Railroad.
Document 12: Magnet, Indiana: Magnet is an unincorporated community along the Ohio River in Union Township, Perry County, in the U.S. state of Indiana.
Document 13: Madison, Indiana: Madison is a city in and the county seat of Jefferson County, Indiana, United States, along the Ohio River. Its estimated population was 12,247 as of 2016. Over 55,000 people live within 15 miles of downtown Madison. Madison is the largest city along the Ohio River between Louisville, Kentucky and Cincinnati, Ohio. Madison is one of the core cities of the Louisville-Elizabethtown-Madison metroplex, an area with a population of approximately 1.5 million. In 2006, the majority of Madison's downtown area was designated the largest contiguous National Historic Landmark in the United States—133 blocks of the downtown area is known as the Madison Historic Landmark District.
Document 14: Mississippi River: The Mississippi River is the chief river of the second-largest drainage system on the North American continent, second only to the Hudson Bay drainage system. Flowing entirely in the United States (although its drainage basin reaches into Canada), it rises in northern Minnesota and meanders slowly southwards for 2320 mi to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains all or parts of 31 U.S. states and 2 Canadian provinces between the Rocky and Appalachian Mountains. The Mississippi ranks as the fourth-longest and fifteenth-largest river in the world by discharge. The river either borders or passes through the states of Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.
Document 15: Metropolitan School District of Mt. Vernon: The Metropolitan School District of Mt. Vernon, Indiana, also known as simply the MSD of Mt. Vernon, is the school corporation serving the City of Mt. Vernon and southern Posey County and is the larger of two school districts in the county. Four townships make up the district: Black, Lynn, Marrs and Point. The largest city is Mount Vernon, Indiana. Tom Kopatich is the superintendent.
ground_truth: Perry County