America is a vast conspiracy to make you happy.The most commonly used term for someone who admires or supports the United States and its culture is an Americanophile (or Americophile).
– John Updike
There does seem to be considerable variation in the spelling/word form. Here is the result of one survey analysing a sample batch of Google searches:
yankophile 945
americanophile 716
americophile 233
americaphile 150
usaphile 14
usphile 1
yankophile 945
americanophile 716
americophile 233
americaphile 150
usaphile 14
usphile 1
'Yankophile' is puzzling as 'yank' is mildly derogatory (albeit often used in jest) in British English.
Comparison with other countries
The words used for fans of French, English, Chinese or Japanese cultureanglophile 102,000, francophile 84,700, japanophile 20,400, sinophile 3450
Why is this?
Increased political polarisation between the US and Europe, plus within individual countries, is clearly one factor. Snobbery/inverted snobbery, perhaps another
Or is it just linguistically awkward - americaphile isn't a pretty word.
(audio) Discussion about the relationship between British and American English here.
(audio) Discussion about the relationship between British and American English here.