Looking for my Benson family in Norway

I'm trying to find the Norwegian roots of my Benson family. My great great grandfather, Biernt E. Benson was born about 1870 in Norway, but I don't know where in Norway. He is listed on the 1880 Dunn Co., Wisconsin census along with his parents, Ingelbrit and Anna, and his 5 younger brothers, all born in Norway. The youngest (twins) are listed as 6 months of age, so I'm concluding that they came over in late 1879 or 1880. I'm having trouble looking on the Digitalarkivet. Does anyone have any tips or suggestions?