Was Jefferson influenced by Locke? Certainly. I don't think there's any doubt he was. But I think it's a serious, almost absurd stretch for anyone to accuse Jefferson of plagiarizing him. One would first have to demonstrate Jefferson's motive in the language he chose was strictly personal, for his own benefit - and while some have attempted to assert that, there are simply no plausible arguments that work in that regard - despite the repeated attempts of some to make such accusations stick.
The language Jefferson employed, indeed the ideas and truths he formalized and put to paper were actually quite common at the time (case in point - SmartCat's post a few posts back), and were bandied about all over the country in various forms of articulation. One might even call them part of the culture of the day. If Jefferson was a plagiarist, then by such standards so is every politician in America today.
Moreover, I think it a serious mistake for anyone to accuse Jefferson of writing for himself. Indeed, I think the evidence is overwhelming that that's precisely what he did NOT do. Did what he wrote receive unanimous accolade? No. Neither did our US Constitution. If it had, we wouldn't have writings such as the Federalist Papers arguing various points of the Constitution.
Personally, I think Jefferson was an excellent writer and thinker. I don't think the thoughts he put to pen and paper in the DoI were all his own; in fact, it's clear they weren't. What he DID do was gather the most salient thoughts and articulate them in a way few others could. What he did write was certainly and unarguably inspired, and that inspiration came from various sources, including himself. What he collected and used, what he discarded, and how he put it all together as a whole was all Jefferson.
And the document itself, as Jefferson articulated it, was, and is, and remains an inspiration to those who agree with the truths and principles therein. Those who disagree with those truths and principles have, and will do whatever they might to disparage it - including disparaging its writer.