At that time it included the current counties of Hedmark , Oppland , Buskerud and Oslo . It also included municipalities of Askim , Eidsberg and TrÃ gstad in the county of Ã stfold . Akershus became a fief in the 16th century , and then also included the current counties of Hedmark , Oppland , Buskerud and Oslo , as well as the municipalities of Askim , Eidsberg and TrÃ gstad in the county of Ã stfold .