The answer is YES!!! Technically the moment you create your work, you own the copyrights to it. However, should your ownership ever come into question, how will you prove that you are indeed the rightful owner? This is why you need to register your copyright declaration as soon as you have completed your book. If you anticipate major structural changes after editing, then wait until you have your polished work. If you are essentially done, go ahead and register your copyright to protect your ownership rights.
Copyright applications can still be done the old fashioned way, by mail. However, with new technology comes progress at the Library of Congress (LOC). The LOC’s United States Copyright office is now online. If you choose to file your copyright applications online, you will not only save money but will also get your certificate faster. Your date of registration will be based on when the Copyright office receives your documentation.