No
Short answer: Never. Old thermostats with mercury switches must be recycled.
NERC's 2020 compendium counts 23 states that ban mercury-containing products from disposal. Montana bans their sale but not landfill disposal. The Thermostat Recycling Corporation runs a national take-back network for mercury thermostats.
Use a Thermostat Recycling Corporation drop-off (often at HVAC wholesalers) or HHW.
Checked October 2026. Rules change; your hauler's prohibited-items list is the final word.