I found an August Brockey in the 1870 CENSUS for Oshkosh, Winnebago Co., WI. He is some kind of a clerk (I can't read the writing) and it says he was born in Prussia:
August Brockey 32 M Single ________ __________ clerk b Prussia, both parents b Prussia.
In the 1900 CENSUS for Wood Lake, Yellow Medicine, Minnesota, I find what must be his sons:
Carl K. Brockey b Jul 1871 Single Head of house b WI Both parents born Norway
August S. Brockey b Apr 1882 Single Brother b MN Both parents b Norway
John E. Brockey b Mar 1878 Single Brother b MN Both parents born Norway
Mary Johansen (?) b Jun 1836 Single Aunt b Norway Both parents b Norway
That makes me think he married in Wisconsin late 1870 (after the 1870 Census) since Carl was born there in Jul 1871. Winnebago County has copies of marriage certificates going back to 1860, but they require a fee ($20) to search. Here is their information.