Combine cucumbers with salt in a large bowl, stir gently, cover, and chill for 1 1/2 hours.
Dump cucumbers in colander, rinse thoroughly well with cool water. Drain and return to bowl.
Add sliced onion to cukes, mix, then transfer to mason jars. Fill to 1/2" under the rim.
In a medium sauce pan over medium high heat, add remaining ingredients and bring to a simmer, stirring until all sugar is dissolved.
Pour vinegar mixture over jarred cucumbers, leave uncovered, and allow to cool to room temperature, about 1 1/2 hours or so.
Cover and refrigerate for 24 hours. They are ready for your enjoyment! Keep in an airtight container in the fridge up to a month.