With any luck, your posting may allow John to connect up his relatives and establish the two of you as relatively [npi] close cousins.
I have some bits of information from Ancestry.com that generally fits your information (and you've likely already seen).Benjamin F. Fallin shows as listed in Oregon Census of 1890 in Douglas County [Felicity Twp.].There is a J.S. Fallin in the Ohio 1840 Census in Clermont County.The 1850 Ohio census apparently shows Ellen Fallin as heading a household in Hamilton County [Cincinnatti} and a Mary (or Maria) in 1860 in the same county.
A list of Civil War Soldiers shows, James, Henry C. and Benjamin F. all serving from Illinois ( Henry C. and Benjamin F. listed as "Musiciians").Benjamin F. is separately lised in a "Muster Roll" as in Company F. of the 48th Illinois Infantry ranked as "1 Cl. Musician."Henry C. is shown the same, as is a David Fallin.I know from direct experience that these lists are spotty for Confederate names, but they are likely better on the Union side.
Now as to David Fallen born ca. 1771 in MD.
I have access to some work done by a member of the MD branch, Kirk Fallin, some years ago. He shows a David Fallin (spelled like that) as the oldest son of Barnaby Fallin.There was a male under 10 listed as part of Barnaby's household in a 1776 Census.He also says "David married Mary Willey in Dorchester County on 11 June 1791.Mary evidently died because David married Esther Purkins in Somerset County on 29 May 1798.David is listed in Somerset County in the 1800 census and no further record has been found of him."I believe I also have Barnaby's antecedents, if this sounds good.I also have references tothe source materials.