Koski Family Genealogy Forum
The names in your query match the names I know in my Koski family. However, the family information is that the name in Finland was actually Myllykoski.
My grandfather was John Koski/Myllykoski who was born in 1879 in Ylistaro, Vassa, Finland. He came to Wakefield, Gogebic County, Michigan in December 1898 with two other Myllykoski men-one Jacob born in 1875 and Matti born in 1877. I am sure Jacob is his brother as they applied for passports at the same time, one #1610 and the other 1611. I think Matti may be a brother also. I do not know of a sister Elizabeth but John had a sister Marie which could be Maija. Did your Jacob have a son Jacob born in 1911? I know some of the members of this family did live in Ohio. I have a reunion article which lists several members of Jacob, Jr.'s family.
My Grandfather moved to Ashland, Wisconsin just prior to the 1910 census. They had a farm at Bass Lake where the family lived until John's death in 1964.