To to this, go to Family Search, go to Search and click Records
On the left hand side of the page, click "United States of America"
So, what did I find?
My great-great-great-grandparents, Gerhardt and Mary Elizabeth Harmeyer in the 1870 census at the bottom of this page:
Finally, while I didn't find this while searching in the censuses, I decided to see if I could find the immigration records for my Bixenman ancestors. I found the ship's passenger list showing my great-grandparents, Benedict Bixenman and Crescentia Wolfgang on the ship Zurich, arriving in New York City on September 7, 1858. Crescentia's last name is spelled "Wolfegg", which, I'm confident, is a phonetic spelling of the way she pronounced it. Some information has said that her actual surname was Wolfeck.