Mention "Oliver Cromwell" and "Ireland" in the same breath and you can be sure to spark a lively debate amongst anyone of Irish descent. Arriving in 1649 to quell the rebellious natives he proved to be not only a ruthlessly efficient military commander but also a potent catalyst in the redistribution of land. The Roundheads were always famously short of money it would appear and solved the problem of paying soldiers by seizing estates and either flogging them off or granting tracts of land in lieu of wages. Restoring the English monarchy doesn't seem to have resulted in any subsequent owners being treated any better if they failed to toe the line either.
Always with the increasingly uneasy feeling that my Protestant Hopkins and Jones ancestors were part of this process, I was intrigued to stumble across this book for free online. The Irish Landed Gentry by John O'Hart was published in 1887. It delves into a broad range of manuscripts, pedigrees and documents from the time of Elizabeth I right through to the late 18th century naming the key players in Irish society as they jostled for power and land throughout this period. Undoubtedly several of the resources he consulted in the late 19th century may not exist anymore so his edited highlights may be the only clues left.
Some of the material is nothing more than a list of names, but some chapters afford more details that might just help to shed light on part of your tree. There is index of surnames so if you are searching for something unusual you may be lucky, else you will have to trawl through a lot of references. However, I would resist the temptation to dive in to this list straight away and spend some time reading the preface section carefully so that you can understand the context in which various records he consulted came to be.