Joe pye weed (Eupatorium species)can get 8-10 feet tall in ideal conditions (plenty of sun and moisture). In less than ideal conditions, more like 6-8 feet. There are dwarf ones too (4-5 feet).

Here's one picture:

{{gwi:834278}}

It depends on which one you're dealing with -- I can think of four Eupatorium species off the top of my head that are called "Joe Pye Weed". Tallest is Eupatorium fistulosum; with ample moisture I've seen it hit 12 feet. E. purpureum and E. maculatum run 6 to 8 feet around here. E. dubium (my favorite) checks in at around 5 feet. There are shorter cultivars, too. E. maculatum 'Gateway' is 5-6 feet tall, and 'Purple Bush' is 3 feet. E. dubium 'Little Joe' gets around 3 feet also.

yikes Oh well it will surely let the neighbor know where my garden is next to his lawn hehehe Does it seed well

Its gateway, I'm lucked out. Can you show me pics of the types so I can tell them apart The biggest to the smallest varities?

Google has an images feature that's great for looking up photos. It brings up clickable thumbnails. I put a link below for what comes up when I used "eupatorium Gateway" for the search words. It tells the image size below each picture.
A couple of people in the past have posted that they had good results when they cut their eupatorium back once in late spring to keep it shorter and bushier. You could try that in the future if it gets taller than you like.

Here is a link that might be useful: Google images - Eupatorium Gateway

Depending upon the species and the growing location it can get very tall.

One way to control its height is to keep it dry or shaded.

But it can also be clipped back and will still bloom. You could clip its height in half, right now, on up to about mid june, and it should still bloom. Keeps it shorter and bushier.

Mine get real tall, 6 to 8' then bend over from the height forming a an upside U shape and new blooms will form at the top of the U. Its very interesting, at least to me. Some gardeners may find that "messy" though.