I inherited stock in a privately held corporation in 2009. The company was sold and I’ve received proceeds. How do I determine my profit?

Gain or loss is the difference between the basis of the stock and what you received for it. The basis of inherited stock used for determining gain or loss is the estate tax value, which is usually the fair market value of the stock on the date of the death of the person you inherited it from. Because such stock is not publicly traded, the way to determine value is to get an appraisal (this would have been done at the time an estate tax return was filed if the value of the entire estate was large enough to require the filing of a return). You can ask the executor if any appraisal was done in 2009. Did other heirs obtain appraisals? Best idea: consult with a tax professional.