I fed them into a concordancer (
CORPUS CONCORDANCE ENGLISH) and got ten examples of "at university" as opposed to none of "in university". However, I got 17 examples of "in college" as opposed to 10 of "at college". Broken down by variety, the results were :
at university - all British English
in college - all but one Am. Eng.
at college - mixed, but twice as many Brit Eng than Am Eng.
I was expecting to find "in school" in Am Eng referring to both grade school and university, but in fact all the examples that came up were for grade school.