This couple can be found in the 1910 census in Spokane. In 1900 they were living in Yellow Medicine County, MN. They are misindexed in the 1880 census under the spelling of Hayes (rather than Hayer as it actually reads) in Benton, Carver Co., MN. He was born in Sachen (Saxony). In 1870 they were living in Benton. He is listed as born in Saxony. The 1860 census lists a Lewis Heyer 30, born in Saxonia, living in Benton.
The 1860 census also includes this family from Minnetonka, Hennepin Co., MN:
Gottlieb Bishop 45, born in Bavaria Catherine 40, ditto Albert 18, born in PA Henry 16, ditto Mary 15, ditto Elizabeth 10, ditto
Whether this Gotleib was related to the Gotleib Biship who died in Philadelphia in 1854 at age 69 years (listed in the 1850 census under the name Gottib Wishoff) I don't know.
Louis and Mary's obituaries would probably help especially to establish he maiden name, any siblings they had and where they were born. Louis probably was naturalized in Minnesota. His papers should have when and where he arrived and perhaps where he was born.