How fast were steam trains?

The railway was not invented until 1825 with the Stockton to Darlington Steam Railway in the United Kingdom. There was a train demonstration in 1805 though. 202km/h is the world record by the LNER Mallard in the UK on 3rd July 1938. The LNER Class A4 4468 Mallard travelled at 202km/h (126mph) in the UK on 3rd July 1938.