The second Earl was Henry Pierrepont, who was born in 1607.  From 1628, when his father was given the earldom, he was known under the style of Viscount Newark.  In that year he was elected Member of Parliament for Nottingham, and he represented that constituency until 1641, when he was summoned to the House of Lords in his father’s barony as Lord Pierrepont.  He, too, was an ardent supporter of the King, and was a member of His Majesty’s Council of War at Oxford.  He was created Marquess of Dorchester in 1645.  After the Restoration he was in high favour at Whitehall.  He was Commissioner of Claims at the Coronation of Charles II, and in 1662 and again in 1673 he acted as Joint Commissioner of the office of Earl Marshal.  He was twice married, but had no direct heirs, and on his death in 1680 the marquessate became extinct.

The earldom passed to the family of the younger brother of the last holder.  This was the great grandfather of Lady Mary, William Pierrepont, who deservedly earned the title of “Wise William.”  He sided with the Parliament, and during the Long Parliament, in the proceedings of which he took an active part, he sat for Great Wenlock.  He was one of the Commissioners selected to treat with Charles in 1642, and after the failure to open negotiations he was anxious to retire from public affairs.  However, he was persuaded not to resign, and in 1644 was appointed one of the Committee of both Kingdoms.  He became a leader of the independent party, and did not always see eye to eye with Cromwell.  He quarrelled with his party, disapproving of its attitude towards Purge’s Pride and the trial of the King.  After this he took little part in politics, though the Protector sought, and he gave on occasions, his advice.  In February, 1660, he was elected to the new Council of State at the head of the list, and in the Convention Parliament represented Nottingham.  In the negotiations with Charles II he was a moderating influence.  Afterwards, he retired into private life.  He died in 1678 or 1679.  His eldest son, Robert, who married Elizabeth, daughter of Sir John Evelyn, pre-deceased his father, dying in 1666, and the earldom passed to his eldest son, Robert, who died unmarried in 1682.  The title then went to his next brother, William, who died without issue eight years later.

A younger brother of Robert and William, Evelyn Pierrepont, now succeeded as (fifth) earl.  He was the father of Lady Mary.  Born in 1665, he was returned to Parliament for East Retford in 1689, but his stay in the House of Commons was brief, for in the following year the peerage descended to him.  In December, 1706, the higher dignity that had once been in his family was revived in his favour, and he was created Earl of Dorchester, with a special remainder, failing heirs male of his body, to his uncle Gervase Pierrepont, who had himself been raised to the peerage as Lord Pierrepont of Ardglass in Ireland and later was given the dignity of Lord Pierrepont of Hanslope in Buckinghamshire.  Lord Pierrepont died in 1715, and both his titles became extinct.