There is a Aaberg family in Otter Tail Co., MN that may be yours.
1930 Fergus Falls, Otter Tail Co., 4th Ward, page 259
Aaberg, Ole K., age 65 born Norway, immigrated 1883
Jena, wife age 63 born Norway, immigrated 1882
Ella J., daughter age 19 born MN
1910 Oscar Township, Otter Tail Co, MN sheet 5B
Aaberg, Ole K., age 45 born Norway, immigrated 1882, farmer
Gina age 43 born Norway
Olive, age 22, born SD
Charles age 18 born SD
Effie age 16 born MN
Olga age 13 born MN
Gina age 10 MN
Bertha age 7 MN
Nora age 5 MN
Floretta age 3 MN
MN Death Index (on-line at
http://www.mnhs.org/library/search/index.htmlAaberg, Ole Knutson, died 9/18/1951 Otter Tail Co.
Aaberg, Mrs. O.K., died 9/11/1936 Otter Tail Co.
Aaberg, Charles born 4/17/1892, died 5/7/1992 Otter Tail Co.,
Mother's maiden name: Kveseth
Olson, Effie G., born 6/28/1894 died 2/6/1995, Otter Tail Co.
Mother's maiden name: Kveseth
Also, see Ancestry Family Trees, which is free at Ancestry.com. There is another person researching this family and has some information posted, including an obituary for Effie Olson that lists her parents, siblings, and children.
Getting the death records and obituaries for this family should give you some additional information and prove out there relationship.