Welcome to the lack of public information for Ireland in the 19th century.
Most census information for 1821 to 1891 was burned offically as well as destroyed during war.
However some information survives as follows.
As per the 1856 Saldanha passenger list Thomas O'Brien profession "Solicitor" was aged 45 yrs so he was born 1811 approx. It also lists his family.
I assume you have the list?
The key to the little information I was able to find is the town of Killaloe, County Clare.
In Slaters directory for Gentry & Clergy for Killaloe in 1846 we find Thomas O'Brien "Attorney" address Kincora which is a suburb of Killaloe town. Kincora may have been his Killaloe business address?.
We also find a Jeremiah O'Brien Esq.,in the same 1846 directory and living in Ryninch which is directly across the river Shannon from Kincora/Killaloe but is actually in County Tipperary.
In Pigot's directory for 1824 there is no mention of Jeremiah or Thomas but it does mention Daniel O'Brien living in Ryninch.
Also be aware that Jeremiah is the English name for "Darby" .
Another suburb of Killaloe is the County Clare townland of "KNOCKYCLOVAUN" and in the Griffith land reports of 1855 we find a Thomas O'Brien owning land and Anne Lockyer owning land.
You can see both directories & the Griffith report free on the Clare County Library. www.clarelibrary.ie
Look up the Genealogy section.