Hill, Mary (1764–1836), marchioness of Downshire , Baroness Sandys of Ombersley in her own right, and noted whig partisan, was born 19 September 1764, daughter and heir of Col. Martin Sandys (d. 26 December 1768), and his wife Mary, daughter and heir of William Trumbull of Easthampstead Park, Berkshire, and his wife Mary, daughter and coheir of Montague, Viscount Blundell. On 29 June 1786 she married Arthur Hill (qv) (1753–1801), earl of Hillsborough, at Lady R. Bertie's house in Mortimer St., Cavendish Square, London. Her father-in-law described the 22-year-old as ‘a genteel, agreeable little girl, not a beauty but as nearly being so as a wise man would choose his wife to be, of a cheerful, sweet disposition’ (1st marquess of Downshire (qv) to Lord Moira (qv), 20 May 1786; Malcomson (1982), 36–7). Furthermore, as contemporaries were quick to remark, she brought considerable wealth to the match. This included a reputed £60,000, Easthampstead Park and over 4,000 acres in Berkshire; Ombersley Court and at least 1,000 acres in Worcestershire; and expectations of inheriting Irish estates at Edenderry, King's Co. (Offaly) (14,000 acres), and Dundrum, Co. Down (5,000 acres). These expectations were realised in 1799.
The marriage was a happy one and the couple oscillated between their town houses in Hanover Square, London, and Gloucester St., Dublin, and their principal English and Irish seats, Hertford and Hillsborough Castles. They had five sons and two daughters, the last son delivered three months after the marquess died of gout of the stomach 7 September 1801. The marchioness attributed the cause of his illness to the mental strain engendered by his dismissal from the post of lord lieutenant of Co. Down and registrar of the court of chancery, and by the division of his regiment, the Downshire militia, into two parts, with a consequent diminution of his patronage and the dismissal of his friends and supporters from official posts. This had been his punishment for refusing to support the Irish act of union.
Her anger at what she perceived to have been unnecessary persecution was not abated by the £52,500 compensation for the seven boroughs owned by the Downshire family which had been disenfranchised at the time of the union, even though this helped to pay off some of her late husband's debts (he died worth a reputed £40,000 a year, but with debts exceeding £300,000), and her elevation to her late paternal grandfather's title as Lady Sandys, baroness of Ombersley, 19 June 1802. (Her father had been the fourth of seven sons of Samuel Sandys, 1st Lord Sandys, and the only one who had children.) Much of her ire was focused on the Stewart family, fellow Co. Down landlords, who had gained control of one of the county seats in 1790 from the Downshires, and of whom a prominent member, Lord Castlereagh (qv), was one of the main protagonists of the act of union. Throughout her son's minority, when she administered the family estates, which in 1801 had a gross income of £34,000, making it one of the wealthiest estates in Ireland, she focused her energies on electoral politics in Co. Down.
In 1802 she agreed to an uncontested election in exchange for her baronage, but in 1805, when Castlereagh was compelled to stand for reelection after he accepted the post of secretary of state for the colonies and the war department in Pitt's administration, she openly opposed him as an ‘inveterate enemy of her family’ (Lady Downshire's memo, 23 July 1805, W. D. Adams MSS, National Archives, Kew). Notices were placed in the Co. Down papers to this effect, and the election became the subject of London gossip and newspaper reports. She made a tour of Co. Down, visiting farmhouses and beseeching wives and sweethearts to exhort their menfolk to vote for Col. John Meade, her chosen candidate. In return she received an ovation at the county town of Downpatrick during the poll. Meade's victory was considered a personal triumph for her. Castlereagh had to find another seat at Boroughbridge, Yorkshire (1806), and Plympton Erle, Devon (1806–12), and did not represent Co. Down again until 1812.
This gave her political control of the two Co. Down seats; Francis Savage had already been the Downshire MP for Co. Down since 1794 and had opposed the act of union. He voted with the opposition until Lady Downshire's rapprochement with the Addington administration in 1802, when she assured Addington he would support the government. Like Lady Downshire, Savage also supported the Grenville ministry and at her wish returned to the opposition when they left government in 1807. He supported catholic claims and Castlereagh's censure for corruption (11 May 1809), and opposed the regency bill (21 January 1811). Meade, who never spoke in parliament, followed a similar voting line.
From the close of the 1805 election until her son's twenty-first birthday Lady Downshire spent the greater part of each year at Hillsborough Lodge, the family's Co. Down seat, a marked contrast to her late husband's predilection for England. There she gained a reputation as a beneficent landlord; as well as individual acts of kindness in 1804 she granted land and £50 towards building the local Roman catholic population a chapel. In order to forward her political influence she also purchased estates at Downpatrick (1805) for £17,450 and Carrickfergus (1807) for £29,000. She also instituted the practice of granting direct leases to subtenants on the Co. Down estates, again to enhance the number of freeholders and potential voters. She granted 486 one-life leases between 1805 and 1807, and by 1809 there were 1,510 tenancies, only 880 of which were long-term. This was famously described by T. H. B. Oldfield in his Representative history of Great Britain and Ireland (6 vols, 1816) as ‘the best specimen of political agronomy to be found in Ireland’ (vi, 227).
In 1809 her eldest son, Arthur Blundell Sandys Trumbull Hill (qv) (1788–1845), 3rd marquess of Downshire, attained his majority. On succeeding to his property he made it his priority to clear the estate of his father's and grandfather's debts as well as the £34,000 in bond and judgement debts accrued by his mother. In order to do so he made an agreement with the Stewart family in 1812 to share the county seats henceforward; Savage was forced to retire and Meade started to vote with the government, although he followed Castlereagh's line on catholic relief. Lady Downshire retired to England, where she was responsible for renovating the parish church of Ombersley. She received a jointure of £5,000 and retained a two-thirds interest in the Edenderry and Dundrum estates, although her son had their entire management. However, his correspondence suggests she continued to take an interest in Co. Down politics.
She died 1 August 1836 after a long illness at Downshire House, Roehampton, Surrey, leaving her title to her second son Arthur Moyses William Hill (1792–1860), who died childless, allowing his younger brother Arthur Marcus Cecil Hill (1798–1863) to inherit.