Webmasters tend to obsess about keyword density and see it as THE key element in on-page SEO. Years ago keyword-stuffing was commonplace and would serve the purpose perfectly adequately of getting web pages ranked for a particular keyword in the search engines.
Thankfully, those days are long gone.
Readability more than anything else is what’s important now. Whilst a keyword density of around just 1 per cent is now often seen as ideal it really does depend on the article and what density competing pages in the search engines have.
See what Google’s Matt Cutts had to say on the subject some time ago:
Matt says that once a keyword has been included in an article once or twice there are usually diminishing returns from any additional inclusions of the keyword thereafter. He emphasises though that there is no golden rule; no optimum percentage. Google just wants us to write naturally for the benefit of the target reader.