When Americans go to university, why do they call it 'going to college'?

"College" and "University" are often used as the same term.

This requires some explanation. When institutions of higher education were first founded in this country, they were all called colleges. The reason was that these relatively small schools with limited courses of study seemed more akin to the individual colleges of Oxford and Cambridge than to universities with many schools and faculties. Harvard College, Yale College, and the College of New Jersey (later called Princeton) were among these early schools.

Over time, as colleges expanded to acquire medical schools, law schools, and other graduate/professional faculties, some adopted the name "university." Smaller schools, however, still tend to be called "colleges," even if they now offer some graduate education. Today, "college" is now used as a sort of generic term for tertiary education, even if the student is actually attending a university.

This site is useful, since it helps explain some historical and contemporary definitions of the word "college":


https://en.wikipedia.org/wiki/College