I have three people I cannot find in the 1870 census.
One I think must have simply been overlooked. She should have been living in southwestern Hancock County, Illinois, in Walker, Rocky Run, or perhaps Warsaw Townships. Sophia Trautvetter was born in 1808 in Germany and was Rocky Run in 1860 with her family in the census. She died in 1877 and is buried in Tioga. I simply cannot find her, but no evidence indicates she returned to Germany or moved elsewhere. Her children were all living in those townships in 1870.
The other two are individuals whom I'm not exactly certain where they lived. Most likely it was west-central Illinois, but they could have temporarily moved further west only to return. Johann Ufkes (born 1838 in Ostfriesland, Germany) and his sister Antje cannot be found. From 1880 until his death in 1924, Johann is in Hancock County, Illinois. He immigrated in 1869 and lived initially in Adams County, Illinois, near Golden. Antje also immigrated before 1870, but cannot be located either.
Searching for the Ufkes siblings is an excellent situation where the researcher needs to track every online search as it is conducted in order to make certain a specific search has not been overlooked. Otherwise it is VERY EASY to go in circles and overlook the same search set of parameters that could be successful. And without tracking how you are searching, it is difficult for anyone to help you and provide suggestions that you have NOT already done.