The title of Earl of Westmeath was created in the Peerage of Ireland in 1621.

The Earl holds the subsidiary title of Baron Delvin (1486).

Barons Delvin (1486)

• William Fitzrichard Nugent, 1st Baron Delvin (?)
• Richard Nugent, 2nd Baron Delvin (?)
• Christopher Nugent, 3rd Baron Delvin (d. c. 1483)
• Richard Nugent, 4th Baron Delvin (d. 1537)
• Richard Nugent, 5th Baron Delvin (1523-1559)
• Christopher Nugent, 6th Baron Delvin (1544-1602)
• Richard Delvin, 7th Baron Delvin (1583-1642) (became Earl of Westmeath in 1621)

Earls of Westmeath (1621)

• Richard Nugent, 1st Earl of Westmeath (1583-1642)
• Richard Nugent, 2nd Earl of Westmeath (1621-1684)
• Richard Nugent, 3rd Earl of Westmeath (d.1714)
• Thomas Nugent, 4th Earl of Westmeath (1669-1752)
• John Nugent, 5th Earl of Westmeath (1671-1754)
• Thomas Nugent, 6th Earl of Westmeath (1714-1792)
• George Frederick Nugent, 7th Earl of Westmeath (1760-1814), elected a Representative Peer in 1800
• George Thomas John Nugent, 1st Marquess of Westmeath, 8th Earl of Westmeath (1785-1871), elected a Representative Peer in 1831
• Anthony Francis Nugent, 9th Earl of Westmeath (1805-1879)
• William St George Nugent, 10th Earl of Westmeath (1832-1883)
• Anthony Francis Nugent, 11th Earl of Westmeath (1870-1933), elected a Representative Peer in 1901
• Gilbert Charles Nugent, 12th Earl of Westmeath (1880-1971)
• William Anthony Nugent, 13th Earl of Westmeath (b. 1928)