This is Tall Bellflower: Campanula americana.
It's wild around here and pops up everywhere, especially in the shaded edges of the woods and roadsides.
An interesting thing about this plant is that it is both annual and biennial. The wiki has details. [Link above]
Down the way from us is a large stand and it is spectacular when it's all blooming at once.
It is indeed tall - most of the plants get around 48 inches tall, even when the year is dry.
