The easiest place to start is the driller's record, because it was written when the well was finished.
1. Look up the state record
If you're in Tennessee, type your address at the top of this page. If there's a record on file, you'll see the depth it lists.
2. Check your home paperwork
Look through closing documents, home inspection reports and old pump invoices. A pump invoice may also show how deep the pump was set, which is not the same as the well depth.
3. Ask the driller or a well contractor
A driller who worked in your area may have the log. A licensed well contractor can also measure the depth on site.
Don't measure it yourself
A line lowered into a well can snag on the pump wiring or introduce contamination, so leave this job to a well professional.
If there's no record
Older wells may never have had a record filed, and some records have errors. Wells nearby can give you a rough idea, but depth can vary a lot over a short distance.