Electricity from geothermal energy was first produced in 1904 in Italy. But geothermal energy was used in the heyday of the Roman empore. The Romans used geothermally heated water to treat certain illnesses and for underfloor heating. The First Nations or Native Americans are known to have used geothermal energy as far back as 8,000 B.C. Today, electricity from geothermal energy is now produced in more than 20 countries around the world, accounting for more than 7,000 megawatts of our global electricity provision.

(Source: http://www.renewable-energy-site.co.uk/facts-on-geothermal-energy.php)