According to the information I found, there are three rivers in the United States that flow north, one is the St. John's River (FL), another is the Willamette River (OR), the third is the Fox River (WI), but just in some points of its basin.
According to WorldAtlas.com there are at least 20 rivers in the U.S. that flow south to north. Here is the excerpt taken from their website on 3/22/2010:
"We make no copyright claim on any statistical data on this page."
Athabasca Alberta, Canada, 765 miles
Bann Northern Ireland
Bighorn Wyoming and Montana, USA, 336 miles
Cauca Colombia, 597 miles
Deschutes Oregon, USA, 250 miles
Eel Northern California, USA, 78 miles
Erne Ireland and Northern Ireland, 60 miles
Essequibo Guyana, 600 miles
Genesee New York, USA, 144 miles
Jordan Utah, USA, 45 miles
Lena Russian Federation, 2735 miles
Little Bighorn, Wyoming and Montana, USA, 80 miles
Magdalena Colombia, 1062 miles
Mojave Southern California, USA, 100 miles
Monongahela Eastern USA, 128 miles
New Virginia and West Virginia, USA, 255 miles
Niagara Lake Erie to Lake Ontario, 39 miles.
Nile Africa, 4150 miles
Ob Russian Federation, 2289 miles
Oswego New York, USA, 24 miles
Otter Creek Vermont, USA, 75 miles
Pend Oreille Washington, USA, 62 miles
Red Minnesota, North Dakota, USA (into Canada), 318 miles
Richelieu Quebec, Canada, 208 miles
Saginaw Michigan, USA, 20 miles.
Saint Johns Florida, USA, 275 miles
San Pedro Mexico (into Arizona), 142 miles
Shennandoah Virginia and West Virginia, USA, 55 miles
Wilamette Oregon, USA, 188 miles
Wallkill New Jersey, USA, length unknown
Yenisey Russian Federation, 2548 miles
Youghiogheny Eastern USA, 151 miles
Mississippi River
The Missouri River is the longest north to south river in the United States. It is 2,341 miles in length.
Mississippi
The Mississippi River is the longest north/south river in North America.
The answer is the Mississippi River. It is around 2340 miles long. Situates in the North- South of the US
south
mississippi
You can cross the US by river only if you are going north to south (south to north is harder) but not if you are going east to west, or west to east.
the mississippi river is the largest in america
The Mississippi River. It is about 2,320 miles (3,730 km) long, and runs from Lake Itasca, MN to about 100 miles south of New Orleans, LA into the Gulf of Mexico.
The Mississippi.
The Mississippi.