I think it may depend on your community? I was called in for jury duty earlier this month. That is, I was part of the pool, though I didn't make it onto a case. On two of the days I went in, I wore business casual attire and was definitely one of the more formally dressed people in the room. Lots of folks wore jeans of various levels of niceness, and there were even some folks in more casual clothes, like leggings. This was in the PNW.
I did wear jeans on one day myself, though that day I also wore a blazer and a nice shirt. But I enjoy dressing up a bit. Also, I planned to go into work on any days I was dismissed early, so I didn't want to wear a completely casual outfit.
If you're selected for an actual jury, you could always ask the jury administrator if more formal clothes are appropriate for being in court while the case is actually conducted. Though my experience with jury duty is that they will usually tell you what you need to know for that sort of thing.