As was evident from the Introductory segment of "Writing a Business Plan", there are a wide variety of formats that can be used in writing a plan. Included here is a broad outline of the type of information that should be included in the plan. Much of the content will be generated by the individual who is trying to make a case for going into business. At certain intervals, where appropriate, you will find resources that might come in handy to expand on those topics.
Consult the guide, How to Find Company Information to find sources to answer these topics.
If you are creating a business plan for a new business, you should be prepared to answer the following questions:
Consult the guide, How to Find Industry Information to find sources to answer these topics:
Consult the guide, Conducting Marketing Research, to find sources to answer these topics:
The U.S. government has a myriad of departments that are good resources to find information on the topics below. Check this excellent A-Z Index of U.S. Government Departments and Agencies.