I haven't yet found any McHaggs in the 1871 Censuses, but I may have done in 1861. Thomas McHagg is in the English Census living in York, East Riding of Yorkshire. He was 58, so born in 1803. He in all likelihood was the father of Frances whom we find in Virginia, USA. More interestingly, according to the 'findmypast' website, there is a family of McHaggs to which the siblings Mary, John and Peter might have belonged, and they lived in Kirkmichael in Ayrshire, and I had been assuming that all clan members had disappeared from Kirkmichael! The family were John (65), Isabella (61), Isabella (20) and David R. (2). It is unlikely that a 59 year old Isabella would have given birth to a baby, so we may assume that David R. was the illegitimate son of young Isabella when she was 18. The 'R' is probably the clue to the surname 0of the father.
Now I have recorded the above, which I have noted from the 'findmypast' website, in part to show how careful we must be to check our sources. I went to the 'ScotlandsPeople' website to view the original census page for Kirkmichael.. The family's address was 91, New Village, and the surname is clearly not McHagg, but is either McHaig or McHarg. ScotlandsPeople thinks it is McHaig. It could well be of course that the siblings in Dudley are also McHaig or McHarg.
Before I found this original I was going to make a suggestion - which I'll make anyway - that John and Isabella, born respectively in nearby Straiton and Ayr, might possibly have been the only John and Isabella marriage I have on record for that period, namely John McIlhague who married Isabella McCallum who had a daughter Jean on 8 March 1824. Their certain link to our clan is that Isabella's brother Alexander married Elizabeth the daughter of James McElhago and Jane Harvey of Irvine. There is also a possible further link that I have pointed out in a previous blog, that John McIlhague may be the same John who later married a Jean Glen in Greenock. If this were so, then we might assume that Isabella had died, perhaps in chiuldbirth. Had the McHaigs really been McHaggs, I was going to point out this possible second marriage to show that John and Isabella McIlhague couldn't be the same as John and Isabella 'McHagg' in 1861, but of course I don't have to do so now, as the 'McHaggs' were in fact 'McHaigs'!