If I speak frankly, Keyword Density does not matter for updated Google Algorithm. What do I mean that Keyword density is the thing which you can check at the last of your SEO campaign? It is just a myth that we should check and give preference to keyword density in our website content. I do not understand why people take care about keyword density in their website content or any other type of content.
I have been promoted as a content head in my company to manage all the writers and their write-ups. I have made a special strategy and content writing guidelines for our writers, so that they can understand the updated SEO writing strategy. I told everyone that does not care about keywords. Just write for users. You can check at the last to verify once about your targeted niche. You can use your primary and long tail keywords naturally. If you will have keywords in your mind, you will start stuffing those keywords. So do remember topics rather than keywords.
Keywords used in On-page SEO
As far as On-page SEO is concern, you should use your keywords in Title, Meta Description, headings, within your contents naturally. You have to use some keyword related images within your content. Sometimes Google does not show your exact title and description from your Meta tags, it takes from your content, menu or side bars. If your website is relevant in specific search terms, you do not have to worry about that. Therefore, you should exactly worry about your content relevancy and quality rather than their keywords and all that. http://moz.com/community/q/keyword-density-clarification-please
What is the ideal keyword density of a page? by Matt Cutts
Keyword Targeting, Density, and Cannibalization – MOZ Whiteboard Friday