Noble titles created in 1800

Marquess of Sligo is a title in the Peerage of Ireland. It was created in 1800 for John Browne, 3rd Earl of Altamont. The Marquess holds the subsidiary titles of Baron Mount Eagle, of Westport in the County of Mayo (created 10 September 1760), Viscount Westport, of Westport in the County of Mayo (created 24 August 1768), Earl of Altamont, in the County of Mayo (created 4 December 1771), Earl of Clanricarde (created 1800) and Baron Monteagle, of Westport in the County of Mayo (created 20 February 1806). All these titles are in the Peerage of Ireland, except the Barony of Monteagle, which is in the Peerage of the United Kingdom. The latter peerage entitled the Marquesses to a seat in the House of Lords prior to the House of Lords Act 1999. The Earldom of Clanricarde was inherited by the sixth Marquess in 1916 according to a special remainder in the letters patent.

Baron Dufferin and Claneboye, of Ballyleidy and Killyleagh in County Down, Northern Ireland, is a title in the Peerage of Ireland. It was created on 30 July 1800 for Dame Dorcas Blackwood, widow of Sir John Blackwood, 2nd Baronet, Member of the Irish Parliament for Killyleagh and Bangor, in return for support for the Union of Ireland and the United Kingdom.

Earl Cadogan is a title that has been created twice in the Peerage of Great Britain for the Cadogan family. The second creation, in 1800, was for Charles Cadogan, 3rd Baron Cadogan.

Baron Tara was a title that was created twice in the Peerage of Ireland. It was created for the first time in 1691 in favour of the soldier Lord Meinhardt Schomberg, younger son of Frederick Schomberg, 1st Duke of Schomberg. He was made Earl of Bangor and Duke of Leinster at the same time. For more information on this creation, see Duke of Schomberg.

Earl of Clanricarde (klan-RIK-ard; Irish: Iarla na Clanricard) is a title that has been created twice in the Peerage of Ireland, first in 1543 and again in 1800. The former creation became extinct in 1916 while the 1800 creation is extant and held by the Marquess of Sligo since 1916.

Marquess of Headfort is a title in the Peerage of Ireland. It was created in 1800 for Thomas Taylour, 2nd Earl of Bective.

Marquess of Ely, of the County of Wexford, is a title in the Peerage of Ireland. It was created in 1800 for Charles Loftus, 1st Earl of Ely. He was born Charles Tottenham, the son of Sir John Tottenham, 1st Baronet, who had been created a baronet, of Tottenham Green in the County of Wexford, in the Baronetage of Ireland in 1780, by Elizabeth, daughter of Nicholas Loftus, 1st Viscount Loftus, sister and heiress of Henry Loftus, 1st Earl of Ely (see Viscount Loftus and Earl of Ely for earlier history of the Loftus family).

Baron Whitworth was a title that was created twice in the Peerage of Ireland. The first creation came in 1721 when Charles Whitworth was made Baron Whitworth, of Galway. He was childless and the title became extinct on his death in 1725. The second creation came in 1800 when Sir Charles Whitworth was made Baron Whitworth, of Newport Pratt in the County of Mayo. He was the son of Sir Charles Whitworth, nephew and namesake of the first Baron of the 1721 creation. For more information on the second creation, see Charles Whitworth, 1st Earl Whitworth.

Baron Ventry, of Ventry in the County of Kerry, is a title in the Peerage of Ireland.

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 (which was that of his maternal grandfather; see below). 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.