Old Gathers
In the late 1990s and early 2000s, like so much else about the otherkin community of the time, gathers were multiplying and thriving as more people decided to start one in whatever location they were in. Alas, there was a decline in the later 2000s. I don't have a unified theory about why this happened, but two things I think were factors were 1. the economic crisis of 2008 and its aftermath that made it harder and harder for many otherkin to afford to travel; and 2. the rise of sites like Facebook and Twitter that drew off so much of people's attention whilst offering little or no privacy (or even provision) for groups, which meant that the lists and boards that had provided the population base for gathers to draw on themselves declined and often either were deleted or at least died out in terms of activity.

Walking the Thresholds (A) (June 1998-2016) - As far as I know, the first, and definitely the longest-running otherkin gather. Organized by Rialian and Yldann/Helen. Its first event was set for June 1998 at Four Quarters Farm in Pennsylvania, but because of some disagreements between its organizers, that year there were actuallly two gathers, held in different locations on the same weekend (see Walking the Thresholds B, below). Here are two Usenet posts advertising it: rec.arts.comics.elfquest December 1997, alt.vampyres March 1998. I don't know of a capture of a page for that first year's event, but here's one from February 2000 that refers to Thresholds 2 in 1999 (which was my first event).
Walking the Thresholds (B) (June 1998) - The other Thresholds was held in Ohio: alt.community.intentional June 1998, and some replies on alt.pagan.magick June 1998 (which apparently involved crossposts to rec.arts.comics.elfquest). Organized by Syleniel (Sileniel) Se'len'na, and I think sade wolfkitten (the sati laughingcoyote of these announcements).
Dancing the Endless Dream (May 1999-2009) - Held in Texas at a variety of locations, mostly near Houston in later years but earlier events were more towards Austin or between Austin and Dallas. Organized by Syleniel (Sileniel) Se'len'na. See also the web page for the first event in 1999.
Kinvention North (January 1999, March 2000-2005) - Held in Kitchener, Ontario. Organized by Ky'Sian and Polydorases. See also the site for the 2001 event.
KinSouth Swamp Gather (October? 2002-2008) - Held in Florida. Organized by Kausha/Spearcarrier.
Dancing the Endless Dream 2 (October 2001) --> F.A.E. Retreat (August/September 2002-2006) - Held mostly near Houston, Texas. Organized by Melishal'Qug. I haven't yet been able to find any still viewable link for the FAE Retreat specifically. For later events it's quite possible information was only visible if logged in to the site as a member. The August 2002 calendar on the FAE site shows that the first event existed on that year's Labor Day weekend, but the pages behind the links haven't been captured.
Dance of the Danu (July 2005) - Held in Virginia. Organized by Lugh and Rhianna SilEl.
Hollow Hills (November 2005) --> MythiCalia (September 2007/2009/2010) - Held in the south San Francisco Bay area, California. Organized by Arethinn. The lateness in the year of the first event was partly born out of my desperation to get something done before I went off to live in Canada in the spring of 2006, plus not previously having known about the lead time one needed to get a specific date for a group campsite at state/county parks in the area (anywhere from 6-12 months). I wasn't in California in September 2006, but I'm no longer sure what caused the dropping of 2008; my recollection is it just kinda didn't happen. Difficulties in attracting registrations for both 2011 and 2012 led me to finally definitively cancel (or at least indefinitely suspend) it thereafter.
A Gathering Echo (September 2007-2018) - The successor to the FAE Retreat, organized by some of the same people and held in the same location near Houston, Texas. Organized by Dan O'Dea and Sidhelady/Georgia. In later years became not strictly an otherkin gather, but more about metaphysics and energy work and open to other groups such as local Druids, although otherkin still made up a good proportion of the attendance.
Company of Others (July 2007) - Held near Centralia, Washington. Organized by Lupa and Erelin.
Crossing the Thresholds (September 2006-2016) - Held at Four Quarters Farm in Pennsylvania. Organized first by Jade and Rialian and passed through several hands before ending up in the charge of Willow and Mark Cat by 2013. An autumn parallel to Walking the Thresholds, hence the similar name. See also crossingthethresholds.
Summer Gateways (May 2010-2017) - The successor to Dancing the Endless Dream, organized by some of the same people and held in the same location near Houston, Texas. Organized by Dan O'Dea and Sidhelady/Georgia. Like A Gathering Echo, in later years this was not strictly an otherkin gather, but oriented towards general metaphysical topics with a fairly large proportion of otherkin attending.
Feywood (July 2011) - Held at the same site as Company of Others, in Washington. Organized by Arethinn. Things were cheaper up in the Pacific Northwest, so for a while I had a dream of running gathers both up there and down in California at different times of the year. Feywood did all right (although there were some hiccups and schedule upsets), but like MythiCalia, at that time in history it was just getting harder to generate and sustain interest in a traditional gather, especially a new event vs. a continuing one.
Dreamhaven (July 2012) - Held in Harrisburg, Pennsylvania. Organized by Jarandhel Dreamsinger and Arial Rainfire.
last updated 8/17/2021