I had the pleasure of seeing one land and take off in Bangor, Maine several years ago. Someone said that there was only one in service. A quick Google search revealed this from Wikipedia:
The An-225 first flew on
December 21,
1988. Two aircraft were ordered, but only one An-225 (
tail number UR-82060
[3]) is currently in service. It is commercially available for carrying ultra-heavy and oversize freight, up to 250,000 kg (550,000 lb) internally
[2] or 200,000 kg (440,000 lb) on the upper fuselage. Cargo on the upper fuselage can be 70 m long.
[4] A second An-225 was partially built during the late 1980s for use by the
Soviet space program. Following the collapse of the Soviet Union in 1990 and the cancellation of the Buran space program, the lone operational An-225 was placed in storage. The six Lotarev engines were removed for use on An-124s, and the second An-225 airframe (nearing completion and awaiting engines) was also mothballed.
.....By
2000, it had become apparent that the demand for the An-225 had exceeded the airline's booking capacity, and in
September 2006 the decision was made to complete the second An-225. Assembly should be completed by
2008.