This weeks episode of the American version of Who Do You Think You Are focused on the paternal ancestry of actor Chris O'Donnell. With a surname like that I was hopeful that the show might focus on where his ancestors came from in Ireland.
On his tree it was outlined that, along with O'Donnell, he had names such as MacCabe, McEnnis, and McNair. The episode focused on two men, his great-great-grandfather Michael McEnnis, from St. Louis, and an even older ancestor George McNair, from Baltimore. The central theme of the episode was the military service of these two ancestors; McEnnis fought in the Mexican-American War and McNair in the War of 1812.
The smart money would say that Chris O'Donnell's ancestors had links with Ulster and various Scots-Irish immigrants. In the show one document outlined that his McEnnis ancestor was the ninth generation of his family to have lived in the U.S., meaning that the original ancestor came to America sometime in the early 18th or even 17th century. These four surnames can also be linked to Ulster and its various counties; McNair as a branch of the Scottish MacNaughton clan found in Ulster, O'Donnell to Donegal, McEnnis to Down, and MacCabe to Cavan.
The 1850 U.S. federal census image for Michael McEnnis that was shown in the show didn't focus on the section that listed his wife Eliza as having been born in Ireland. His mother, also Elizabeth McEnnis, listed as living in the same dwelling, had a number of probable borders born in Ireland. They could possibly be relations from the old country.
No mention was made of any place in Ireland that an ancestor was from. Of course, there could be a number of reasons for this. It might have been omitted for editorial reasons, or maybe it was not discovered. The second reason is quite plausible as finding the Irish place of origin can be difficult, especially if the various branches of O'Donnell's family came to the U.S. in the years before the American Revolutionary War.
Has anyone discovered they are related to Chris O'Donnell, or more importantly when any of your shared Irish ancestors are from?
 MacLysaght, Edward. 1985. p.85 / This would be a common Irish name and McLysaght further outlines that it also has strong associations with Clare and Galway
 MacLysaght. 1985. p. 140 / This is probably one of the many versions of the name commonly represented as MacGuinness e.g. McGennis, Magennis etc..
 Familysearch.org, 1850 US Federal Census, St. Louis County, Missouri, population schedule, 6th Ward, City of St. Louis, page unknown, house number 543, family number 623; McEnnis family, Michael and Eliza McEnnis and Family; digital image, Familysearch.org https://familysearch.org/pal:/MM9.3.1/TH-266-11128-45190-45?cc=1401638&wc=MMY6-7BF:n1654688373: accessed 21 August 2013; LDS microfilm number 443626