Syllable Stress Analysis by Tom Zurinskas http://truespel.com 
The data here involves the top 5,00 words of English and number of instances in text counted for them according to Collins Cobuild. There are 15.4 million instances of these words taken from typical text, which I estimate make up about 90% of words on a typical text page (books newspapers etc.). The results for syllable stress for US accent show that:
1. Of the 5,000 words 1,457 (29%) are single syllable, but they make up 73% of words in text (11.3 M out of 15.4 M instances) .
2. The remaining 27% of words of typical text are multisyllable words (4.1 M instances).
3. The 27% breaks down into 19% with first syllable stress and 8% with other syllables stress.
4. Thus, for all multi-syllable words in text, about 70% (19/27) have stress on the first syllable and 30% (8/27) have stress on other than the first syllable