Lynn,
There’s a long answer to your question and a short one. I’d say you need the short one.
Most of Ireland gained independence from the UK in 1922 and was then known as the Irish Free State. 6 counties remained part of the UK (Antrim, Down, Armagh, Tyrone, Fermanagh & Londonderry/Derry) and were/are known as Northern Ireland. In 1949 the Irish Free State left the British Commonwealth and formally became known as the Republic of Ireland (or just Ireland for most practical purposes).
Your ancestor who gave “Free State of Ireland” as their place of birth in 1930 was therefore saying they were from the 26 counties that now form the Republic of Ireland. That narrows your search a bit but still leaves a wide area.