After finding the grave of Margareth yesterday, I started doing some more research on the Maisenbacher family in Illinois. I already knew that Anna Maisenbacher (later Mehl) had two sisters and a brother. We have an oral history of the family, given by Frances Mehl in 1974 and taped by Bill Mehl. In that history, Frances names Anna's two sisters - Mary and Lizzy - and her brother, John. Frances thought John was the youngest, but in fact Anna was the youngest, born in 1865 while her father John was away fighting the Civil War. The names and ages of the oldest three children appear in the 1860 Census, when the "Meisenberger" family was living in Rahway NJ. John Jr was 6, Mary was 3, and Elizabeth was 9 months old when the 1860 census was taken in June 1860. (If you are looking it up, the index on Ancestry.com uses the spelling Meisenberger for the 1860 record. Other sites may have different spellings.)
According to Frances, Anna was born in New Jersey, so I made the assumption that the family moved to Illinois sometime after 1865. Also according to Frances, Anna lived with Frank Markert as a child. I have an old postcard that shows Frank's address as Bath, Illinois. So I started looking for them there in 1870. No luck with any spelling of the Maisenbacher name, or with the Frank Markert. So I went through Bath Township census page by page, line by line.
The Bath Township census is only 54 pages, but it took awhile. I found Lizzy, age 10, living with Lawrence Westerburger, his wife Amelia, and their one year old son. She is simply listed as "Living with Family." I also found Mary living with George Markert, his wife Elizabeth, and their son Francis. 14. Francis (Frank!) was born in New Jersey. So now I know Frank is about the same age as Mary, and that the Markerts and Maisenbachers may have known each other in New Jersey.
Sadly, I found no trace of Margereth and John Maisenbacher, or the five year old Anna, anywhere in the country in 1870. I found a John Maisenbacher (indexed as Meisenbachez) in New York City, right age, and from the right place, but he has a different wife and different children, so not likely to be related. I have not done a page by page review of Mercer County yet, but that may be a reasonable next step. Where did they go?
Followup on the Maisenbacher sisters: from Frances' oral history, we know that Lizzie Maisenbacher married Charles Potts, and Mary married Ludwig Voigt. Both marriages are registered in the Mason County, IL marriage registers.