At http://detcon1.org/ I noticed that they gave last weekend's attendance:

Detcon1

The North American Science Fiction Convention Rocked Detroit!

Thank you to everyone who came out and contributed to a fabulous NASFiC.
The total number of attending memberships was 1628, with a warm body count
of 1450, making Detcon1 the largest Science Fiction convention in Michigan – so far!

As far as two other Michigan cons: I don't recall the attendance numbers for the 2013 ConFusion, the last I attended, but I want to say is was around 800?

Penguicon Attendance, 1,377 (2014)

The last two Worldcons were North American -- hence no NASFiC needed -- and attendance was pushing 5000. One expects Loncon 3 in London next month to be lower?

70th Worldcon - Chicon 7 - 30 Aug-3 Sep 2012 - Chicago, IL
4,743 attending/6,197 supporting

71st Worldcon - LoneStarCon 3 - 29 Aug-2 Sep 2013 - San Antonio, TX
4832/6130

By contrast, the results from Detroit 55 years ago:

17th Worldcon - Detention - 4-7 Sep 1959 - Detroit MI
371 attending

Data from the Long List of Worldcons.

The last two NASFiCs with attendance data were:

8th NASFiC - CascadiaCon - 1-5 Sep 2005 - Seattle, Washington
1785/2014

10th NASFiC - Reconstruction - 5-8 Aug 2010 - Raleigh, NC
~750/~900

Data from the Long List of NASFiCs.

So, the 11th NASFiC - Detcon1 - Detroit MI was a clearly a success for the participants and a success by any other measure as well.

Well done, Detcon1 !

Dr. Phil