Dedham grammar school was founded by letters patent from the crown dated 14 May 1575, enrolled on membrane 17 of what is now filed as PRO C66/1136. It is calendared thus in CPR (1572–75) (London, HMSO, 1973).

3270) 14 May 1575. Grant that there shall be a free grammar school in [m.17 contd.] Dedham, co. Essex, to be called the free grammar school of Queen Elizabeth in Dedham. Appointment of Edward Walgrave of Lawford, co. Essex, Edward Waldegrave, his son and heir apparent, Robert Gurdon of Asshington [recte Assington], co. Suffolk, John Gurdon, his son and heir apparent, William Cardinale [sic] of Bromley Magna, John Worthe, vicar of Dedham, William Butter, Pierce Butter, his son, Ralph Sterlinge, Robert Sterlinge, Richard Sterlinge, Robert's son, John Browne the elder, John Browne, his son, Michael Upcher, Richard Upcher, his son, Henry Sherman the elder, Henry Sherman the younger, his son, Edmund Sherman, also Henry's son, Louis Sperhawke, Nathaniel Sperhawke, his son, John Upcher, Robert Luffkyn, John Wood and Richard Wood, his son, to be governors.

Incorporation of the governors. Whenever a governor shall die, the survivors may elect another inhabitant of the town in his place. Licence for the governors to hold certain lands (named) in Bradfeild [recte Bradfield] and Wrabnes [recte Wrabness], co. Essex, and such other lands as shall hereafter be conveyed to them, to the yearly value of £40, so that they be not held of the Crown in chief or by knight service. Power for the governors to make orders and rules for the government of the school, and to acquire lands without fine or fee for the Queen's licence in this behalf.

William Lyttlebury late of Dedham by his will desired that, for the instruction of the youth of the same town and of Ardley [recte Ardleigh], Great Bromley, co. Essex, and Stratford, co. Suffolk, and the relief of the poor of Dedham, a free grammar school should be founded in Dedham, for the maintenance of which he gave to the persons above-named (except Worthe) the said lands in Bradfield and Wrabnes. By Q.