I recently did some research online in anticipation of the 20 year anniversary of Sluggy Freelance (woohoo!), and I believe I have found some cool news. From what I can tell, Sluggy is the 5th oldest, and still-running webcomic on these here Internets~
The order of webcomics (with Date of creation and URL) is as follows:
1) Bob the Angry Flower (Sometime in 1992)*
http://www.angryflower.com/2) Kevin & Kell (Sunday, September 3, 1995)
http://www.kevinandkell.com3) Help Desk (Sunday, March 31, 1996)
https://www.eviscerati.org/comics4) Nukees (Tuesday, January 21, 1997)
http://www.nukees.com5) Sluggy Freelance (Monday , August 25, 1997)
http://sluggy.com/*Apologies for vagueness, but archives, the website, and other sources are unspecific *~*
**Piled Higher and Deeper (or PHD) is a close contender, being created on October 27, 1997
I used TV Tropes, Wikipedia, and the comicsites themselves as sources. If I am or this list is wrong in anyway, then please don't hesitate to correct me.
P.S. I'm still relatively new to the forum, so this post may be in the wrong place/not follow regulations.
Happy 20 Years!