Samuel and Eleanor (Riddle) Mills did indeed emigrate, to the United States. There are several trees on the 'Ancestry' website setting out aspects of their life there, though the usual health warning applies regarding the accuracy of such uploaded information - 'Caveat lector!'
In these trees, Eleanor is named Ellen Elenor Mills, before marrying Samuel Mills, she is shown as having married a John Thomas Moffitt in 1835, and having had children John (1836), George (1838), and Ann Jane (1840), before her husband John Thomas died in 1840 - sources not checked. But lots more such information is covered, should you wish to look at it (with that health warning).
However, one intriguing aspect is a reference to an obituary in the Coshocton Age (Ohio) of 28 November 1886, which is the source of a birth year of 1813 for Ellen and
may be the source of County Monaghan as her birthplace. I say 'may', for I haven't read the obituary, but that is the birthplace stated in at least one of the trees.
Anyhow, in that light, I mention the following two baptisms, in the Donagh St. Salvator parish church (Church of Ireland) at Glasslough, County Monaghan, for a couple named Petter and Sarah Riddell of Pullis:
- George Riddell baptised on 13 November 1801;
- Sarah Riddell baptised on 8 April 1804.
These are the only baptisms I could find for this couple, as always, that may simply reflect them having moved elsewhere, for which the local parish records aren't online. BTW, there was quite a cluster of Riddells in that part of County Monaghan, for example, in the same townland of Pullis, there was a couple named John and Elizabeth Riddell with the following children baptised in the Donagh St. Salvator parish church: Sarah in 1798, Oliver in 1803, Elizabeth in 1805, and Thomas in 1813. The Tithe Applotment Books show a John Riddell in Pullis (1826), I couldn't find 'Petter' (or Peter).
Pullis is about 12 miles south of the action thus far (ie. from the area just north of Ballygawley):
https://www.townlands.ie/monaghan/trough/donagh/emyvale/pullis/So really just no more than a possibility to note for now.