Bell Bar is a hamlet located in North Mymms, Hertfordshire, England. It is in the civil parish of North Mymms. Thought to be named after the ancient Bell Inn which stood nearby, Bell Bar (often spelt as "Bell Barr" on old maps, such as that of Emanuel Bowen, c. 1720) was a cluster of dwellings around this coaching inn on the Great North Road (United Kingdom) which used to pass through Bell Bar along what is now called Bell Lane. However, in 1851 the route of this road (now the A1000 road) was altered to avoid the steep hill to the south of the hamlet and to avoid cutting through the grounds of Hatfield House.