The MDUA was established in 1967 to officiate Baltimore City baseball games.
There are over 110 active members within the MDUA. Many officiate 5 or more games a week.
The MDUA services over 80 schools spanning as far west as Frederick and as far east as Easton.
The Mason Dixon Umpires Association (MDUA) provides umpire services for Baltimore Metro area schools beyond. These schools include the Maryland Interscholastic Athletic Association (MIAA), Maryland Public Secondary Schools Athletic Association (MPSSAA) in Baltimore County, Baltimore City, Carroll County, Frederick County, Maryland Independent Athletic Conference (MIAC), and Maryland Association of Christian Schools Athletic Conference (MACSAC).