* Public vs. Private: Private colleges and universities are significantly more expensive than public institutions.
* In-state vs. Out-of-state: Public universities charge out-of-state students much higher tuition than in-state residents.
* Type of Institution: Tuition at a large research university will generally be different from a small liberal arts college.
* Program of Study: Some programs (like medicine or engineering) are often more expensive than others (like humanities).
Therefore, you'll find widely varying averages depending on the source and how they define "average." You might see numbers ranging from a few thousand dollars per year at a low-cost community college to over $60,000 per year at a prestigious private university.
To find a relevant average, you need to specify the criteria: For example, "average tuition at a four-year public university for in-state students in [State]" would yield a more meaningful result. You could then use resources like the College Board's website or the National Center for Education Statistics (NCES) to find this data.