Hi, PTOMOM2016! Congrats on taking this step to formalize your organization!
The short answer is: You do NOT need to be incorporated to apply for 501(c)(3) status. 501(c)(3) is a federal designation that your group is exempt from paying federal income tax. Incorporation is a state-level designation that indicates how your organization is formed as a legal entity. The way you prove to the IRS that you have been in existence for the past few years is by filling out the application with your historical information (financial, mostly) for the years in question.
Here's the longer answer: Why not go ahead and incorporate first? It's a pretty short application in New York State. There is a $75 filing fee, but it then makes you eligible to receive state and local tax exemptions (income, sales, and use taxes) -- so it's a good investment for the long term. And, it will make it easier to fill out your 501(c)(3) paperwork because you won't have to include the historical financial info -- you will be a brand-new organization with no history in the eyes of the IRS as of the date of incorporation.
Here are some links to help you:
Tax-Exemption and Nonprofit Status: What PTOs Should Know
-- This PTOtoday.com article explains a few key terms and walks through the steps to incorporate and file for federal tax-exempt status.
How To Form a Nonprofit Organization in New York State
-- This is info from ny.gov that outlines the steps for your state.
Not-for-Profit Corporations FAQs
-- This is on the website for the New York State Department of State, Division of Corporations. If you click on the "more" link in the question I linked to, it has links for the fillable online incorporation application as well as instructions.
Good luck!
Lani @ PTO Today