Bluestar - Amsonia tabernaemontana

Also may be called Blue Dogbane.
Note: This is native to central and southern Illinois, though not the greater Cook County area. See map below.

Features: The attractive blue flower clusters make this a striking addition to a rain garden or woodland edge. Tubular flowers may attract hummingbirds, as well as offer pollen to bees, butterflies and moths. Host to the Coral Hairstreak butterfly's caterpillar.

Each flower is replaced by an interesting twin seed pod. Foliage may turn a pretty yellow in the fall. Can form a 3x3 foot mound after a few years. 

Light: Sun to Partial shade

Soil: Medium

Height: 2-3 feet

Blooms: May

See more information and photos at: Illinois Wildflowers and Missouri Botanical Garden 

Photos 1-3 Illinois Wildflowers, 4 Wikipedia, 5 BONAP