Hi MLou,
You most likely already have this information but here is the McNamara family living in Wauwatosa Township in Wisconsin in the 1860 census. From the location of the birth of their 12 year old son Dennis in Ireland, and 10 year old daughter in Wisconsin, it looks like the family emigrated about 1849 or 1850? The father Dennis was only 50 years old in 1860, so born about 1810.
https://familysearch.org/ark:/61903/1:1:MW9W-7C5
Have you found any record of the eldest son John in the 1860 census? Was he old enough to fight in the American Civil War? If so, there might be pension records that have information on his birth.
In addition to the 3 sons born in Ireland, have a look for the Wisconsin death records for the parents. Also obituary records in the local newspaper might have detail where exactly in Ireland they are from.
From this 1851 newspaper account, it looks like the father Dennis McNamara was a newspaper subscriber and perhaps still adjusting to life on the wide open prairies of Wisconsin:
Milwaukee Sentinel, December 29, 1851 (genealogybank.com newspaper archive)
STRAYED.
Came into the inclosure of the subscriber on
or about the first of November, an old red
COW - white striped on her back and very large
horns. The owner is requested to prove property,
pay charges, and take her away. DENNIS McNAMARA
Wauwatosa, south of the Spring Street Road
Have you had any luck finding their immigration records? McNamara is such a common name that it could be difficult. But if they were traveling as a family of five and since you know the year 1849 / 1850 you should be able to find them. Perhaps they were traveling with a group of families from Clare which could provide a clue where they were from - especially if it was an organized emigration.
The Milwaukee Sentinel newspaper in August 1849 had an advertisement that made reference to the creation of an office of the Irish Emigration Society in Milwaukee that was ready to take orders for the sale of lands. Once approved the different lots would be advertised in the Irish papers for 3 months for the benefit of the Society which consists of several hundred Irish families of respectability and capital...