Nancy Piatt was born May 13, 1824, in Pennsylvania (probably Lycoming County) to William and Mary Brady Piatt and died August 23, 1864. She married c1846 (probably Lycoming County, Pennsylvania) Robert H McCormick who was born c1822 in Pennsylvania and died sometime after 1880. I would guess that he was the son of the Hannah McCormick born c1790 in Pennsylvania who appeared with his family on the 1850 census.
Nancy's parents were in Washington County, Lycoming County, Pennsylvania on the 1830, 1840 and 1850 census.
The known children of Nancy and Robert are:
Brady Piatt McCormick b: 1 Feb 1847 PA d: 15 Apr 1871
Hannah M McCormick b: 30 Nov 1848 PA d: 4 Feb 1891
William E McCormick b: 10 Nov 1850 d: 8 Sep 1862 (not on 1860 census with family)
Mary P McCormick b: 15 Mar 1853 d: 26 Mar 1857
Joseph/James H McCormick b: 10 May 1855 PA
Margaret McCormick b: 11 Mar 1857 d: 25 Nov 1858
Robert W McCormick b: 4 Aug 1859 PA d: 28 Apr 1864
Frances 'Fannie' J H McCormick b: 10 Sep 1861 PA
Robert and family were on the 1850 census of Delaware Township, Northumberland County, Pennsylvania:
McCormick, Robert H age 27 born PA / wm / Merchant
McCormick, Nancy age 26 born PA / wf
McCormick, Brady P age 4 born PA / wm
McCormick, Hannah M age 2 born PA / wf
Bower, Barbara age 20 born PA / wf
McCormick, Hannah age 60 born PA / wf
This family was enumerated #278/280 pg 20A (Ancestry.com image 39/46).
I next locate Robert and family on the 1860 census in McEwensville, Northumberland County, Pennsylvania, as follows:
McCormick, Robert age 38 born PA / wm / merchant / $3000/$20000
McCormick, Nancy age 37 born PA / wf
McCormick, Brady age 13 born PA / wm / att school
McCormick, Hannah H age 11 born PA / wf / att school
McCormick, James H age 6 born PA / wm / att school
McCormick, Robert age 10/12 born PA / wm
Piatt, Mary age 75 born PA / wf
Mengas/Menyas, Catharine age 17 born PA / wf
This family was enumerated 771/758 pg 368 (Ancestry.com image 1/10). Edward Derickson and William Hayes were next door neighbors. I'm sure the Catherine Manger age 7 in 1850 living with William and Mary Piatt in Lycoming County, Pennsylvania, is the Catharine Mengas age 17 on this census. Was she a family member? Nancy's sister-in-law, Lydia Piatt (widow of Brady Piatt) and her brother, Samuel T Piatt, were in Lycoming County, but, soon after the census removed to Northumberland County.
Nancy died in 1864 and Robert and their remaining children appeared with Nancy's sister on the 1870 census of Watsontown, Northumberland County, Pennsylvania:
Hammond, Fannie B age 60 born PA / wf / keeping house / $5000/$500
McCormick, Robert age 47 born PA / wm / salesman
McCormick, Brady P age 22 born PA / wm / bookkeeper
McCormick, Hannah age 20 born PA / wf / without occupation
McCormick, James age 14 born PA / wm / at home / att school
McCormick, Fannie J age 9 born PA / wf / at home / att school
Piatt, Samuel T age 47 born PA / wm / at home
This family was enumerated #188/223 pg 191B (Ancestry.com image 28/30); near John H and Sarah Foresman. On page 186 was the family of Lydia Wetzell Piatt.
They were still in Watsontown for the 1880 census:
Hammond, Fanny B age 70 born PA / WWF / Keeping House / father born NJ/mother born PA
Piatt, Samuel T (Brother) age 57 born PA / SWM / Gentleman / father born NJ/mother born PA
McCormick, Robert H (BroL) age 57 born PA / WWM / Dry Goods Merchant / father/mother born PA
McCormick, Hannah M (Niece) age 31 born PA / SWF / father/mother born PA
McCormick, James H (Nephew) age 25 born PA / SWM / Druggist / father/mother born PA
McCormick, Frances J H (Niece) age 18 born PA / SWF / At Home / father/mother born PA
This abstract was taken from Familysearch.org; pg 208B. I did not view the actual entry. Still living in Watsontown (but very near together this time) on page 210B was the family of Lydia Wetzell Piatt.