I'm at my grandfather's funeral today, and literally half the people there were wearing something I thought was completely inappropriate. One dude was wearing a fucking batman T-shirt and fucking jeans. My cousin was in a full blown cowboy get up complete with jeans, flannel, cowboy hat and boots with a giant ass belt buckle. Keep in mind this kid was born and raised in northern Michigan. He hasn't rode a horse a day in his life.
Now I'm not expecting everyone to show up in a suit and tie but to me, jeans are absolutely unacceptable funeral attire.
In the South dressing up is still big/expected although some funerals especially really big ones during the week many aren't held up to a super exacting standard especially if the electrician or construction or whoever has to go right back to work. In those cases most bring a nice shirt to swap into but you may still catch some jeans and work boots.