I know someone called Jeremiah, Albert (which was also my dad's middle name) and Herbert (in fact, I know two people called Herbert). And one of my mates has named his baby Nathaniel.
So, perhaps the names aren't dying out that quickly.
Not a name that is commonly found, but noteworthy for all that. A search of http://freebmd.rootsweb.com/cgi/search.pl reveals that there were just FIVE Victorians named after the famed biblical wanker.
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Births Mar 1839
Onan Kershaw Bradford
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Births Mar 1842
Onan Wickham East Grinstead
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Births Dec 1856
Onan Browne Depwade
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Births Jun 1865
Onan Marlow Bicester
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Births Dec 1889
Onan William Jones Stourbridge
I once wrote to John Peel's Home Truths programme about this. He read my message out.