Here are some resources that are available to those looking for help or information on mental illnesses. Please note that if you are in crisis, it is best to contact your local emergency services: dial 911 here in the US. I am happy to include regional resources around the world here, so if you would like to see a particular resource here, please let me know in the comments.
United States
988 Suicide & Crisis Lifeline

The 988 Suicide & Crisis Lifeline is a national network of local crisis centers that provides free and confidential emotional support to people in suicidal crisis or emotional distress 24 hours a day, 7 days a week in the United States. We’re committed to improving crisis services and advancing suicide prevention by empowering individuals, advancing professional best practices, and building awareness.
Note: 988 is now active across the United States. This new, shorter phone number will make it easier for people to remember and access mental health crisis services. (Please note, the previous 1-800-273-TALK (8255) number will continue to function indefinitely.)
Make It OK

“Make It OK” is a campaign to reduce the stigma of mental illnesses. They work to change the hearts and minds about the misperceptions of mental illnesses by encouraging open conversations and education on the topic.
The Make It OK campaign is made possible by HealthPartners, Inc.
National Alliance on Mental Illness

NAMI, the National Alliance on Mental Illness, is the United States’ largest grassroots mental health organization dedicated to building better lives for the millions of Americans affected by mental illness.
Canada
I got these resources from Nesi :verified: 𓃧 ☥ (@Nesi@pagan.plus) – Mastodon
Call 1-888-668-6810 or text WELLNESS to 686868 for #youth
Call 1-866-585-0445 or text WELLNESS to 741741 for #adults
#KidsHelpPhone: Call 1-800-668-6868 (toll-free) or text CONNECT to 686868
For #FirstNations, #Inuit, and #Métis Peoples, Call 1-855-242-3310 (toll-free) or connect to the online Hope for Wellness chat (https://www.hopeforwellness.ca/)
National Indian Residential School Crisis Line: 1-866-925-4419
Missing and Murdered Indigenous Women and Girls Crisis Line: 1-844-413-6649