Looking for Ellefson's

I need some help tracing my husbands line. He's from Minnesota, and I have been able to trace back to Engebret Ellefson, B. 1848 in Norway. According to the US census for 1880, he was in Goodhue, Minnesota, in 1980 (at this time his oldest child, is three and listed as having a MN birthplace, so it's safe to say that Engebret was in MN as of 1877 at the latest.) My issue is that no matter how hard I look, I can't find anything to tie Engebret to ANY other previous Ellefson, Ellevsen, Ellefsen, Olsen from Norway. If there is anything anyone can think of to help I'd really appreciate it...I'm going nuts over this Thanks. St