Baron Henniker, of Stratford-upon-Slaney in the County of Wicklow, is a title in the Peerage of Ireland. It was created in 1800 for Sir John Henniker, 2nd Baronet, who had previously represented Sudbury and Dover in the House of Commons. His son, the second Baron, also sat as a Member of Parliament. In 1792 he assumed by Royal licence the additional surname of Major. He was childless and was succeeded by his nephew, the third Baron. He assumed the additional surname of Major by Royal licence in 1822. His son, the fourth Baron, represented Suffolk East in Parliament. In 1866 he was created Baron Hartismere, of Hartismere in the County of Suffolk, in the Peerage of the United Kingdom. This title gave him and his descendants an automatic seat in the House of Lords. He was succeeded by his son, the fifth Baron. He also sat as Member of Parliament for Suffolk East and later held minor office in the Conservative administrations of Benjamin Disraeli and Lord Salisbury. His grandson, the eighth Baron, was a prominent diplomat and notably served as British Ambassador to Jordan and to Denmark. As of 2014 the titles are held by the latter's son, the ninth Baron, who succeeded in 2004.

Stratford-on-Slaney, also known as Stratford or Stratford-upon-Slaney, is a small village on the River Slaney in west County Wicklow in Ireland. It was built by the Earl of Aldborough from 1774. According to the census, the village had a population of 241.