"Massachusetts Births and Christenings, 1639-1915," database, FamilySearch (https://familysearch.org/pal:/MM9.1.1/FZ86-BM3 : 10 February 2018), Mary L. Derby, 1843; citing LEOMINSTER,WORCESTER,MASSACHUSETTS, ; FHL microfilm 0874029 IT 2.
"Massachusetts Births and Christenings, 1639-1915," database, FamilySearch (https://familysearch.org/pal:/MM9.1.1/FZ86-BMQ : 10 February 2018), Cephas Derby in entry for Mary L. Derby, 1843; citing LEOMINSTER,WORCESTER,MASSACHUSETTS, ; FHL microfilm 0874029 IT 2.
"United States Census, 1850," database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MD9W-N8P : 12 April 2016), Mary S Derby in household of Cephas Derby, Leominster, Worcester, Massachusetts, United States; citing family 589, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).
Find A Grave, database and images (https://www.findagrave.com : accessed 05 May 2018), memorial page for Mary L Derby (1843–1855), Find A Grave: Memorial #27311184, citing Evergreen Cemetery, Leominster, Worcester County, Massachusetts, USA ; Maintained by jandal (contributor 47013996) .