Family #24 in the 1767 Grimm census.
Family #107 in the 1775 Grimm census.
August Hartmann Rusch was born about 1688 in the Pommern area of what is now Germany. Samuel Rusch, who appears with him in the Grimm 1767 and 1775 censuses was probably his brother. His middle name is listed as Hartmann in the 1767 census, and Ertmann [sic] in the 1775 census. Although his middle name was probably Hartmann, in Grimm that name was spelled phonetically as Ertmann and later Erdmann.
In the birth record for his son Ernest Christian, he is shown as being from Wulkenzin. 
According to Wikipedia:
This matches what he and his brother told Russian census takers, that they were from the general area of Pommern.
August and his family do not appear in the Kulberg List of German immigrants to Russia,  nor do they appear in the Transportation List that documents the travelers from Saint Petersburg to the Volga region of Russia.  Nonetheless, the family shows up in the 1767 Grimm census as some of the first settlers of Grimm.
1767 Grimm Census 
According to the American Historical Society of Germans from Russia, The Rusch family from Grimm was from Pommern and Schlitz, Germany.  I have been unable to find any birth or marriage records for him in Pommern, Schlitz, and all of Germany through the Family Search.org database.
August and Katharina's marriage was perhaps a second marriage for August. There was a 30-year age difference between August and Katharina. His marriage to Christina would have been his second or third marriage. There was an 19-year age difference between the two wives. Christina was probably not the mother of any of his children, as the youngest she would have been when they married was 60.
August could have very easily had grown children who did not immigrate with him to Russia, as he was about 70 years old when he arrived in Grimm. His age is off between the two censuses.
Most likely there was a typo or transcription error in one of the censuses
1775 Grimm Census 
Note that his daughter Christina does not appear in this census. In 1775, she would have been around 17. She was most likely married and living in another household.
Also note that both of his wives, Katharina and Christina, had the same surname, Engel. They are not the same person, however, because Katharina was 30 years younger than her husband, and Christina was only 11 years younger. It's possible they were sisters or cousins, but just as likely they were unrelated.
August Rusch does not appear in the 1798 census, and he had most likely passed away by that year. Had he survived, he would have been 110 years old (or 100), which is very improbable. He probably died close to 1775 than to 1798.
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