Rodskasa Farm - Skeberg - Jensen, Eriksen

My great-grandfather was Anton Eriksen, born Dec. 1st 1858, son of Erik Jensen. Their family farm was in Skeberg (Ostfold). I have the 1865 census listing - Anton was 7. His father, Erik Jensen was 49. How can I find out more about them? Can someone help point me to other sources? Thanks! Alice Eriksen