When was the last time minnesota won the big ten in football?

Answer 1

1988.

Prior to NIU's win over Purdue on September 19, 2009 their record against Big 10 teams was 1-32-1. Their only other victory came against Wisconsin, 19-17, on September 17, 1988 in Madison.

Answer 2

Prior to the 2008 and 2009 seasons when Illinois defeated Michigan 45-20 and 38-13, that was 1957 and 1958 when Illinois won 20-19 in Champaign and 21-8 in Ann Arbor.

Answer 3

1967 when they were Big 10 co-champions with Indiana.