AngieJohnston - 3:06 am on Jun 4, 2013 (gmt 0)
No, to my understanding it's the entire body of text. They lend more importance to the subheads because users do, too (that's why they need to relate to your page's content really well, and if you're location-based, include that if it won't disrupt the flow of text).
You want the opening paragraph to clearly state what your page is about, which is where your keyword(s) can be used. Remember that Google delivers results that aren't always based on exact phrases, too--so if your keyword was NYC Lawyer Food-borne Illness, you can say "I'm a NYC lawyer who works on food-borne illness cases every day."
After that's done, build your page on giving your readers what no one else is: information. That lawyer will say things like "Spending two years in litigation" and "When you appear in court." Google knows this and it recognizes that you've built an informative page that readers want to see, versus your competition who just has some contact information and a bunch of garbage (like a list of terms at the bottom of the page that says "NYC Lawyer | Lawyer New York | Hire a Lawyer in SoHo" or is engaging in other black-hat type stuff.
I hope that helps! :)