New rules governing drone ownership require anyone aged 13 or over who owns one of the craft to add their details to the register.
Anyone who gets a drone after 21 December must register with the Federal Aviation Administration (FAA) before it goes on its maiden flight.
Existing owners have until 19 February to put their details online. Anyone who does not comply could face hefty fines.
Those who register will be given an identification number that they must display on the remote-controlled craft. Registration is valid for three years.
The rules cover drones weighing between half a pound and 55lb (228g to 22.7kg).
A $5 (Â£3.30) registration fee is being waived for the first 30 days of the system to encourage people to register. Those who do not comply could face a fine of up to $27,500.
The FAA hs said that in "severe cases" of drone abuse it can mount a criminal prosecution which could see offenders hit with a $250,000 fine and up to three years in prison.
The register of owners has been set up following several high-profile cases which saw drones flown in restricted airspace near airports and crowds, or that interfered with the work of emergency services.
The FAA said it wanted the register up and working before Christmas as drones are widely expected to be a popular gift.
FAA rules for flying drones stipulate that they must:
A US government registration system for Americans who own drones has gone live.