According to the Oxford English Corpus 'millennium' and 'fahrenheit' are amongst the top misspelled words in English language ('millenium' and 'farenheit' are the common misspellings).
Surprisingly, as Google Trends show, New York, London and Chicago - regions where English is the first language - are among the top 10 regions accounting for these misspellings.
Google Trends
The Oxford English Corpus