What happens when a company I invested in goes out of business? Is that declared as a personal capital loss? Does it offset capital gains elsewhere, and how do I include it in my tax filing?
If this was a public corporation (stock) and the investment was made in a non-registered account, then you can claim a capital loss. Capital losses are claimed against capital gains (not income), and can be carried back 3 years or carried forward indefinitely.
Here's an article I've written on how to claim capital losses that may help.
Since you say the money was invested in a corporation that would lead me to believe you mean a stock purchase. Stock losses can be treated as a tax exemption filed as a capital loss.
Canada has slightly more restrictions on how this can be done.