That's hardly unusual. A quick Google search turned up the following...
95% answered "very happy" or "fairly happy" in 2003.
96% answered "very happy" or "fairly happy" in 2006.
Unfortunately, the Gallup poll asked this question (happiness) irregularly from 1948-1996, and only started asking this every year since 2000. However, they have asked a similar question about "being satisfied with the way things are going in their personal lives" on a regular basis, and...
"Americans have always reported a high level of personal satisfaction -- at least 8 in 10 have said so since 1993 (Gallup has asked this question since 1979). The lowest level of personal satisfaction Gallup has ever recorded was still robust -- 73% in July 1979." (from 2006)
We should also probably notice that there's a difference between being "happy" in response to a general question versus being "happy" about the state of the nation (America's greatness, which was the initial genesis of this particular tangent). Today, I am very happy with my personal life; I have a pretty good job, married to a lovely woman, things are going well in my hobbies. Am I happy with the state of our federal government? Not really. Incidentally, the same Gallup poll from 2006 which found 96% of people reported being "very happy" or "fairly happy" and 84% said that they were "very satisfied" or "satisfied" with their personal lives also asked about satisfaction with the way things are going in the United States. Let's see how that went.
"That stands in stark contrast to the 30% of Americans who say they are satisfied with the way things are going in the United States at this time. There have been several times in Gallup's polling history when there have been larger gaps between personal and national satisfaction, with the largest being a 64-point gap between personal (81%) and national (17%) satisfaction in January 1981." (again, this was from 2006)
So, being happy with your personal life /=/ being happy with the state of the nation. Mmmmk?
Since we're on the subject of Gallup polls, let's also check in on what they say about our current President:
"President Donald Trump's 40% job approval rating about one month into his presidency is 21 percentage points below the historical average rating for elected presidents in mid-February (61%). It is also 11 points below the lowest mid-February reading for any other president."