The middle name of “Julian” is from the death records for the infant twins who died in 1855. Their birth records list their mother’s maiden name as Rosanna Walton, and their death records list their parents as “Wm & Julian Downing”.

I have not been able to determine her parents. There were no Walton families in Morgan Co of the appropriate generation in the 1840 or 1850 censuses. There were, however, a very large number of Walton families in Fleming Co., too many to choose from. Land and estate records might yield useful information, but almost none of those are available online, and are tedious to search by microfilm since each reel usually only holds a few years.

Morgan Co. marriage register 1, on LDS Film 839,918, records marriage of William M. Downing and Rosanna Walton on 1 Sep 1844 by Thomas Easterling.

1850 census of Morgan Co., Ky, lists family #1165:
William Downing, 27; Rebecca, 25; William, 4; Mary, 2; Eliza, 1. All born in Ky.

The birth records for Julian and Newton born in May 1855 list their mother as Rosanna Walton, which agrees with the 1844 marriage record, so the “Rebecca” must be simply an error.

1860 census of Trenton township, Grundy Co., Missouri, enumerated 11 June, lists on p. 48 as family #418/365:
Wm Downing, 38, farmer; Rosana, 36; Wm. D., 15; Mary J., 13; Eliza, 11; Nancy, 9. All born in Kentucky.

The preceding household is for James F. Downing, age 36.

Nancy’s name falls on the last line of the last page for this township, but it does not contain the usual notation that “here ends the ...”

Then, on the last page of the census for Washington township of Grundy Co., enumerated by the same clerk in mid-July, is the family of a Wm J. Knight, age 43, butcher, born in England, with wife and 4 children, the older 2 and his wife being born in England and the youngest two in Missouri, followed by the line saying “completion of township of Washington”. But then that line has been hash-marked out, and following it are listed:

Clorinda Downing, 7; Henry, 5; Margret, 2. All born in Kentucky.

No household number accompanies the group of Downing children. By comparison with the 1870 census, they are obviously children of William and Rosanna.

And then the “Washington township completed” line is repeated.

This makes it appear as if the Downing children are part of the Wm J. Knight household. But considering the facts that Trenton township enumeration did not end with the customary annotation, and that the Downing children were listed after a “false end” to the enumeration for Washington township, and that William and Rosanna were both alive and their household intact in 1870, and that there is nothing else to indicate any relationship between the Knight and Downing families, I believe that what happened was that something happened to the last page for Trenton township, and that rather than leave them out entirely, the clerk appended the younger children in the William Morrison household who had been on it to the mostly-blank last page for Washington township.

Note also that the ages of Clarinda and Nancy have been traded from what is implied by Morgan Co. birth records and the 1870 census.

1870 census of Liberty township, Grundy Co., Missouri, enumerated 10 August, lists on p. 12 as family #94/91:
Downing, Wm M., 47, farmer & minister; Rosanna J., 46; Clarinda, 19; Nancy A., 17; Henry F., 14; Margaret, 11; Elizabeth, 9; Sarah A., 5. William through Henry born in Kentucky, Margaret through Sarah born in Missouri.

The next household is that of William Hodges age 28 born Illinois with wife Eliza age 21 born in Ky.

The one after that is their son William, listed as age 25, born in Ky, with wife Mary E., age 23, birthplace blank, and son Darius, age 5 months.

William and Rosanna probably both died before 1880, since their three unmarried daughters were all listed that year with older married sisters (Margaret with Eliza, Elizabeth with Mary, and Sarah with Nancy.)