(Undated) -- A new study says the youngest county in each state is often due to the presence of a major college. "24-7 Wall Street" says that's the case in 41 of the 50 states, plus DC. In Oregon, it's Benton County, home of Oregon State University in Corvallis. The average age is just under 33, while the state's median age is 39. The report shows that just under 24 percent of Benton County residents are enrolled in college.