Oh, and remember that TIME cover story on angels, many years ago? (I think that's where I learned that angels are NOT supposed to be spirits of the dead.)
Anyway, from Gallup, in 2016 (trouble is, it doesn't say whether the people they asked understood the above distinction):
...Gallup asked the question that includes the "not sure about" option in random rotation with questions about belief in four other religious concepts: angels, heaven, hell and the devil. Americans' belief in all of these is lower than their belief in God, ranging from 72% who say they believe in angels to 61% who say they believe in the devil, with 12% unsure on both. Belief in these four concepts is down at least marginally from when last measured in 2007, following the same pattern as the trend in belief in God using this question format...