The Regency Period officially started in 1811 when the then Prince of Wales officially became Regent of England when his father George III was formally declared unfit to rule. The period officially ended in 1820 when George III died and the Prince Regent officially became King George IV.
For purposes of genre fiction, Regency encompasses many years on either side, easily up to 1830 when George VI died and his rather austere brother William IV took the throne. It can also stretch backwards easily until 1800, but with deft writing, also into the 1790s as during this time society was still ruled by the Prince Regent, though at times he was not officially titled as such. It is the tone and feel of the period, made popular originally by Jane Austen that dictates whether or not a romance is set in the Regency period.
Some other wonderful writers who set their stories in the Regency period are:
Happy reading, Samantha James