
Joan certainly seems a tough one..
ok, I am starting to get confused, so what do we have for sure?
Her name was definitely Joan Rachel Plunkett Darr , as given in her obituary
She was born about 1915 in York, PA
1920 census: There is no Joan or Rachel Darr, Olevia and Edward Darr are living alone, There is a Rachel R Plunkett (no Joan) living with her father Henry, mother (could anybody read her name on the census?), and siblings.
1930 census: Rachel is living with the Darrs and there is also no sign of her siblings going by the name of Plunkett
She has 2 boys with somebody called Myers
1940 census: again no sign of her and her sons are living with the Darrs.
What happened to the Plunkett parents? Who was Mr.Myers? and where is she in 1940?

I have never done research for the PA area before and google hasn't been too big a help, are there any old newspaper archives online I can look at? Is there any way I can find out if she was adopted?