Looking for any information prior to 1880 on the following people:

John Knapp - born Hesse Darmstadt between 1840-1845 died Iowa County, Wisconsin 1913
Mary Catherine Schmitz (Knapp) born Prussia abt 1850 died Iowa County, Wisconsin 1916
Maria Agnes Zander (Schmitz) born Prussia abt 1810 and died ???? (after 1880) location unknown

John Knapp is shown in the 1880 Census as being born about 1845, In the 1910 Census it shows 1841

His Death Record shows - John Knapp, Laborer, 72y9m22d, died 2-6-1913 at Mineral Point. He was born 4-14-1840 in Germany to George Knapp, born Germany and "don't know" born Germany,

Death record for John Knapp's wife --- Mary Cathryn Knapp, nee Schmitz, age 66y6m19d, born Germany to Peter Schmitz & Mary Agnes Zander also born Germany. Born 1-9-1850 and died July 28, 1916 at Mineral Point

Possibility - 1870 Census - John Knapp born 1843 Darmstadt, resides Wauwatosa, Milwaukee - shows wife Mary C age 20 born Prussia and Daughter Elisabeth age 2 born Wisconsin. There are several Agnes or Mary/Maria Schmitz/Schmidt in the area of Milwaukee or Wauwatosa that could have been her mother.

Cannot find any death record of Maria Agnes Schmitz born about 1810 and died in or near Iowa County, WI She should have died soon after the 1880 census as she was shown as Mary Smith living with John and Mary Knapp in Iowa County.- no further info here. Her husband is supposed to be Peter Schmitz -