An organization called Global Language Monitor estimates there are more than 900,000 words in the English language, and with more are being added every day, this means that some time this year we should hit 1 million.
Of course this is a controversial statement; the Cambridge Encyclopedia of the English Language suggests that there must be at least a million words already and the Oxford Companion to the English Language, comes up with a similar figure. The Cambridge Encyclopedia goes further saying that if you allow all scientific terms the total could easily reach two million.
Either way we have come a long way since 1582, when the English grammarian Richard Mulcaster said that the language was "of small reach, stretching no further than this island of ours, nay not there over all".