There are a wealth of fandom conventions in North America, some conventions have a specific focus (Star Wars, MLP), and some have a more general focus (Anime, Comics). Here are resources about fandom conventions in the USA.
Date: January
Website: https://animelosangeles.org/
Location: Long Beach Convention Center
Attendance Information: 11,961 Unique Attendance (2020)
Fandom Focus: Anime, Manga, and Cosplay
Date: January
Website: https://www.animeimpulse.com/
Location: Pomona Fairplex
Attendance: Unknown
Fandom Focus: Anime, Manga, and Cosplay
Date: February
Website: http://www.gallifreyone.com/
Location: Los Angeles Airport Marriott
Attendance: 3,900 Unique Attendance (2018, attendance capped)
Fandom Focus: Doctor Who
Date: March/April
Website: https://www.comic-con.org/wca
Location: Anaheim Convention Center
Attendance: 66,000 Unique Attendance (2018)
Fandom Focus: Comics, American Animation, and Hollywood
Date: April
Website: https://www.animepasadena.com/
Location: Pasadena Convention Center
Attendance: 5,400 Unique Attendance (2019)
Fandom Focus: Anime, Manga, and Cosplay
Date: May
Website: https://www.comicconrevolution.com/ontario/
Location: Ontario Convention Center
Attendance: 5,449 Paid Attendance (2017)
Fandom Focus: Comic and Sci-Fi
Date: May
Website: https://animeoc.org/
Location: Cal State Fullerton, Titan Student Union
Attendance: Unknown
Fandom Focus: Anime, Manga, and Cosplay
Date: June
Website: https://www.ronin-expo.org/
Location: JACCC Little Tokyo, Los Angeles
Attendance: Unknown
Fandom Focus: Anime, Manga, and Cosplay
Date: July 4th Weekend
Website: https://www.anime-expo.org/
Location: Los Angeles Convention Center
Attendance: 115,000 Unique Attendance, 350,000 Turnstile Attendance (2019)
Fandom Focus: Anime, Manga, and Cosplay
Date: July/August
Website: https://www.animangausa.com/
Location: Ontario Convention Center
Attendance: Unknown
Fandom Focus: Anime, Manga, and Cosplay
Date: September
Website: https://officialpowermorphicon.com/
Location: Pasadena Convention Center
Attendance: Unknown
Fandom Focus: Power Rangers and Super Sentai
Date: September/October
Website: https://www.comicconla.com/
Location: Los Angeles Convention Center
Attendance: 100,000 Unique Attendance (2019)
Fandom Focus: Comics, American Animation, and Hollywood
Date: Winter Convention: January/Summer Convention: September
Website: https://www.sacanime.com/
Location: Cal Expo in Sacramento, CA (Normally Sacramento Convention Center)
Attendance: 21,000 unique attendance (2018)
Fandom Focus: Anime, Manga, and Cosplay
Date: March
Website: https://www.clockworkalchemy.com/
Location: Burlingame Hyatt Regency Hotel
Attendance: Unknown
Fandom Focus: Steampunk
Date: May
Website: https://baycon.org/
Location: San Mateo Marriott San Francisco Airport
Attendance: Unknown
Fandom Focus: SciFi and Fantasy
Date: May
Website: https://www.fanime.com/
Location: San Jose McEnery Convention Center
Attendance: 34,000 Unique Attendance (2019)
Fandom Focus: Anime, Manga, and Cosplay
Date: July
Website: https://www.comic-con.org/cci
Location: San Diego Convention Center
Attendance: 130,000 Unique Attendance (2019, capped)
Fandom Focus: Comics, Sci-Fi, and Hollywood
Date: September
Website: https://expo.crunchyroll.com/
Location: San Jose McEnery Convention Center
Attendance: 45,000 Turnstile Attendance (2018)
Fandom Focus: Anime, Manga, and Cosplay