Whenever another creature or planeswalker you control dies, put a +1/+1 counter on Rising Populace.
If Rising Populace and another creature you control die simultaneously (perhaps because they were both dealt lethal damage in combat), Rising Populace won’t be on the battlefield as its triggered ability resolves. It can’t be saved by the +1/+1 counter that would have been put on it.
If a planeswalker that’s also a creature dies, Rising Populace’s ability triggers only once.