In the last 15 years, the monarch butterfly populations in North America have dwindled to "alarmingly low" levels, University of Guelph associate professor and ecologist Ryan Norris. He was part of a group of researchers who developed a strategy on preserving and improving the monarch’s populations.
Minor edit: If you can, plant some NATIVE milkweed.
A lot of big box stores sell tropical milkweed that can fuck with Monarchs’ natural navigation and migration instincts.