Jacob Listed as Isakson in 1900 & Isacson in Welch Co. in 1910. Isacson, Nils age 55 b. in Norway Im. 1886 married once 14 yrs. Anna age 51 b. in Norway Im. 1896 married 14 yrs had 4 children 2 living Isac age 10 b. in ND. Aron age 8 b. in ND.
I would guess by the Im. years that they married in Welch county ND.