Hi Nancy:
Here is a quick synopsis which I hope that you will find helpful:
townland is the smallest land division in Ireland. It is akin to a neighbourhood. You will find very often (and certainly pre-Famine) that many of these families are not only neighbours but cousins.
The civil parish is the administrative and often old Gaelic territories that were used in medieval times. They can contain a number of townlands (numbers can vary). The English and Church of Ireland used them as administrative units and very often, parish records will use the civil parish name as opposed to the Roman Catholic name. For example, Ennistymon is the Roman Catholic parish, but the civil parish is Kilmanaheen. The civil parishes then make up the Union. The Union is the Poor Law Union which was created in 1838. The purpose of the unit was another administrative division which was used (and the earliest government unit) in Ireland and in England. The Union was a cluster of civil parishes (and a larger cluster of townlands). The Union administered poor laws and later local government laws. Every Union contained a workhouse or some form of poor relief for those residents within the union.
These administrative divisions are still important for research as records are divided within these divisions. The Census and the Civil Registration (Births, Marriages & Deaths) are all based upon Union and therefore important to know.
As an example from my reply above about a Patrick Kane, you will note that one is in the townland of Tullyvarga West, in the civil parish of Kilmanaheen and Union of Ennistymon. The other Kane surnames are in various townlands (Aughinish, New Quay, Rine, Turlough, Aughwillian) in the civil parish of Oughtmama and the Union of Ballyvaughan. This union lies to the north of Ennistymon. It is worth keeping in mind both Unions and Civil parishes when you are looking at records/censuses and other administrative documentation.
I hope that the above helps. There is also a link on the website about townlands which is here: https://irelandxo.com/ireland-xo/news/irelandxo-insight-what-townland
Please let me know if you have any other questions.
All the best,
Jane