WPA records for Allen County show a marriage for George Van Horn and Margaret Parker on 18 February 1886. The 1900 and 1910 census give birth years as about 1863 for George and 1870 for Margaret.
George appears to be the son of George Van Horn born about 1813 in New Jersey and Esther born about 1835 in Canada. You'll find this family in New Haven, Indiana in 1880.
I find a Margaret Parker, age 1, in the household of J.R. Parker and wife, Sophia in Jefferson Township, Allen County in 1870. J.R. was a "Stationery Engineer" - sounds pretty important - but I don't see them in Allen County in 1880.
This should give you some leads to follow - good luck!