The present Marquessate was created in 1793. The Marquess holds the subsidiary titles of Earl of Hertford (Peerage of Great Britain, 1750), Earl of Yarmouth (Peerage of Great Britain, 1793), Viscount Beauchamp of Hache (Peerage of Great Britain, 1750), Baron Conway of Ragley (Peerage of England, 1703), Baron Conway of Killultagh (Peerage of Ireland, 1712). The Marquess's heir uses the style of Earl of Yarmouth.

Table of contents

1 Earls of Hertford, First Creation (1135) 2 Earls of Hertford, Second Creation (1537) 3 Earls of Hertford, Third Creation (1559) 4 Marquesses of Hertford, First Creation (1641) 5 Earls of Hertford, Third Creation (continued) 6 Earls of Hertford, Fourth Creation, Peerage of Great Britain (1750) 7 Marquesses of Hertford, Second Creation, Peerage of Great Britain (1793)

Earls of Hertford, First Creation (1135)

• Richard de Clare, 1st Earl of Hertford (1100-1136)
• Gilbert de Clare, 2nd Earl of Hertford (d.1151)
• Roger de Clare, 3rd Earl of Hertford (d.1173)
• Richard de Clare, 4th Earl of Hertford (1153-1217)
• Gilbert de Clare, 5th Earl of Hertford, 1st Earl of Gloucester (1180-1230)
• Richard de Clare, 6th Earl of Hertford, 2nd Earl of Gloucester (1222-1262)
• Gilbert de Clare, 7th Earl of Hertford, 3rd Earl of Gloucester (1243-1295)
• Ralph de Monthermer, Earl of Hertford and Gloucester (d.1325), acquired Earldoms through marriage to the widow of the 6th Earl, and lost them on her death in 1307.
• Gilbert de Clare, 8th Earl of Hertford, 4th Earl of Gloucester (1291-1314)

• Edward Seymour, 1st Duke of Somerset, 1st Earl of Hertford (1506-1552), forfeit 1552.

• Edward Seymour, 1st Earl of Hertford (1539-1621)
• William Seymour, 2nd Earl of Hertford (1587-1660) (became Marquess of Hertford in 1641)

• William Seymour, 2nd Duke of Somerset, 1st Marquess of Hertford, 2nd Earl of Hertford (1587-1660), restored to the Dukedom of Somerset in 1660.
• William Seymour, 3rd Duke of Somerset, 2nd Marquess of Hertford, 3rd Earl of Hertford (1651-1671)
• John Seymour, 4th Duke of Somerset, 3rd Marquess of Hertford, 4th Earl of Hertford (d. 1675) (Marquessate extinct 1675)

• Francis Seymour, 5th Duke of Somerset, 5th Earl of Hertford (1658-1678)
• Charles Seymour, 6th Duke of Somerset, 6th Earl of Hertford (1662-1748)
• Algernon Seymour, 7th Duke of Somerset, 7th Earl of Hertford (1684-1750)

• Francis Seymour-Conway, 1st Earl of Hertford (1718-1794) (became Marquess in 1793)