I got the land amount from the property tax documents.
Solid proof that you own a portion of the land. Otherwise, you are not assessed a property tax for real estate that you do not own.
I'm confused. 15 years ago, I paid $70,000 for a condo. I don't know the assessed value of the land at the time. (Currently, it is 30% of the 2020 total assessed property value.).
Assessed value is only used for determining what percentage of your purchase price gets allocated to the land. That's it.
I have been depreciating the full purchase price of the condo ($70,000). Have I made a mistake? If so, what should I do moving forward?
You need to fix it, as you have been taking more depreciation each year than you are entitled to. Since you're more than halfway through the class life (27.5 years for rental property) I would highly suggest you seek professional help. This would be especially necessary if your state also taxes personal income. BTW - I always recommend professional help for situations like this if it's been more than 3 years of doing things wrong, for two reasons.
1) TurboTax only supports their product for the current tax filing year and 3 years back. If you use TurboTax to amend or file a return more than 3 years back, chances are high it will be wrong. That's because you flat out can not get the required critical updates and corrections for the TTX program more than three years back.
2) If amending a return more than 3 years back and the amendment will result in a refund, you will not get that refund because of the IRS's three year statute of limitations on that. The amendment may still be needed though, to correct things on the front end. Unfortunately, if amending a return up to 10 years back results in you owing the IRS money, you'll have to pay it plus interest and any fines or penalties that may be assessed. A tax professional may know a few loopholes or work-a-rounds to help with that for all I know.
