How to easily find duplicate values in HUGE spreadsheet

I often run into this issue with things I do on a regular basis for work. I have an extremely large spreadsheet, for example 200,000 lines, and need to find the duplicate values. However, I don't just want to remove the duplicates, I need to see which values were duplicated so I can manually update them in a backend system. Normally I would use conditional formatting to highlight any duplicate values, then sort the column by cell color. When trying to do this on an enormous spreadsheet though, Excel completely freezes. Does anyone know of a better solution?

Thanks for the suggestion! I'm in the process of seeing if Excel can handle it. I wasn't familiar with COUNTIF so tested a small sheet first to make sure I got the results I wanted, and am currently waiting to see how long it takes to filter for the values greater than 1 in the actual document. I expect it will take forever, but hopefully filtering is at least somewhat quicker than sorting!