Keyword density is a myth! Thee search engines don't pay attention to that anymore. They only did in the early days of SEO. Check out this bit from Rand Fishkin of SEOmoz:

"The truth is simply that modern search engines have never used keyword density. Look through any intro to information retrieval course in any university on the planet and you’ll see that it’s been debunked as a high-cost, low return metric. Instead, they use term weight – TF*IDF – check out some good work on the subject from Dr. Edel Garcia (one of the few information retrieval scientists whose crossed over into seo)."

Source: http://www.hobo-web.co.uk/keyword-density-seo-myth/