You do not need to be connected to the internet and/or Steam in order to play PG. However, you will only have access to the default courses that came with the game since a connection to Steam is required to verify any purchased content and user-made courses.
I haven't played offline in a while. Is this still the case?
Unfortunate that a huge percentage of the course library is unavailable if playing offline. Even ones we've purchased or built ourselves? Yikes.
This is the fine print What JoeF and Bortimus said - I ran a test booted up the computer unhooked my Ethernet Cable so in other words the internet is down or I cannot access it, or steam is down, or my modem broke, or I'm in a hotel room without internet access but I have PG so everything is great right ...
Well sort of here is the video:
so even if the internet goes down and your pc was off you can go into offline mode without connecting to steam and choosing offline mode but as stated with other posts you are limited to only the stock courses. Its kind of like back in the old days when we only had a few courses to play even though we knew there were other courses out there but they had not been released yet and when Course Forge was just a dream ....
ok so anyway what this also means is that even if you have made a course with CF you cannot play your own course. You cannot play other peoples courses even if you have them saved to your hard drive. Would be nice if Steam and or Perfect Parallel ever for whatever reason abandoned perfect golf that one could at least make a golf course themselves and hot seat play it with a friend the only thing one could do is play the stock courses.
.... although I'm slightly worried at how uncannily accurate those facts are 
