In 1865, the Civil War ended, and at that time, there was one Lynn High School which was located near the old Registry of Motor Vehicles on Mont Vernon Street. In 1887, ground was broken for the first Lynn English High School near the old school administration building and the Boys & Girls Club on Franklin Street. The building was completed and graduated its first class in 1889. Shortly thereafter in 1891, 31 students formed the Lynn English High School Alumni Association, Inc. and elected its first president and staff members.

Lynn English High School was eventually re-located four additional times. The second location existed from 1889 to 1892 in the old wooden frame building now known as Girls, Inc. of Lynn on High Street. From 1892 to 1924, Lynn English occupied the building which became Cobbett Junior High School and is now an apartment complex on Baldwin Street. From 1924 to 1931, Lynn English moved next door into the building which later became the Lynn Trade School. Lynn English has been in its current location since 1931.

It is believed that the alumni association is the oldest continuously active alumni association in the United States with no break in service since its founding. On June 21, 1927, the association became a nonprofit corporation known as the Lynn English High School Alumni Association Inc. Years later, the name was changed to Lynn English Alumni Association (LEAA). This name change was made to put the school alumni on recognizable par with Boston English and Boston Latin. There are currently an estimated 70,000 alumni.