Question: The Aeolian Singers are based in the English county bordered by which county on its north?

Context articles: Katesgrove
Hertfordshire
Aeolian Singers
Barnby Broad and Marshes
Castle Bromwich
Abbey (Reading ward)
Basildon, Berkshire
Popovo (župa)
Park (Reading ward)
Kentwood (Reading ward)

Katesgrove is an inner-town district near the centre of the town of Reading in the English county of Berkshire and ward of the Borough of Reading, in the English county of Berkshire.
 It is bounded on the north by the Inner Distribution Road and Reading town centre, on the east by Sidmouth Street, London Road, Kendrick Road and Northumberland Avenue, on the west Coley Park and Southcote, on the south by Long Barn Lane and Rose Kiln Lane and on the west by the River Kennet.
Hertfordshire ( ; often abbreviated Herts) is a county in southern England, bordered by Bedfordshire to the north, Cambridgeshire to the north-east, Essex to the east, Buckinghamshire to the west and Greater London to the south.
 For government statistical purposes, it is placed in the East of England region.
The Aeolian Singers, president Peter Skellern, musical director Stephen Jones, rehearsal pianist Anna Le Hair, was established in 1963.
 With about 80 members, it is Hemel Hempstead's largest mixed-voice chorus.
 While based in Hertfordshire, the singers also perform in major London concert halls and in other parts of Europe.
 In recent years they have performed in Ghent, Paris and Provence and visited Mannheim in October 2006, where they performed in two concerts together with the Konzertchor der Stadt Mannheim.
 They have a very wide repertoire ranging from Renaissance to contemporary music, and have given several first performances.
 They also have a tradition of community and youth involvement.
Barnby Broad and Marshes is a Site of Special Scientific Interest (SSSI) in the Waveney district of the English county of Suffolk.
 The site is 189.6 ha in size.
 It is in the parishes of North Cove and Barnby, located between Beccles and Lowestoft in the north of the county.
 The site is bordered on its southern edge by the East Suffolk railway line and to the north by the River Waveney.
 It is a Special Area of Conservation, a Special Protection Area under the EC Birds Directive, and a Ramsar internationally important wetland site.
 There are two Suffolk Wildlife Trust nature reserves in the site, Castle Marshes and North Cove.
Castle Bromwich ( ) is a suburb situated within Solihull in the English county of the West Midlands.
 It is bordered by the rest of the borough to the south east, North Warwickshire to the east and north east; also Shard End to the south west, Castle Vale, Erdington and Minworth to the north and Hodge Hill to the west – all areas of the City of Birmingham.
 It constitutes a civil parish which had a population of 11,857 according to the 2001 census, falling to 11,217 at the 2011 census.
Abbey is an electoral ward of the Borough of Reading, in the English county of Berkshire.
 The ward covers the centre of the town, south of the River Thames, and is bordered by Battle, Park, Redlands, Katesgrove and Minster wards.
 Across the river it is bordered by Thames and Caversham wards.
 The ruins of Reading Abbey lie within the boundaries of the ward, a fact from which it derives its name.
Basildon is a civil parish in the English county of Berkshire.
 It comprises the small villages of Upper Basildon and Lower Basildon, named for their respective heights above the River Thames.
 Basildon is 7 mi from Reading, 47 mi from London and 20 mi from Oxford.
 The parish is bordered to the north by the River Thames and the Oxfordshire parishes of Goring and Whitchurch-on-Thames on the other side of the river.
 To the south of the river it is bordered by the parishes of Pangbourne, Bradfield, Ashampstead and Streatley.
 The parish forms part of the unitary authority of West Berkshire.
 It is within the Newbury parliamentary constituency.
In the Middle Ages, the territory of the Popovo field by the Trebišnjica, the northern part of the Ljubinje area, and the southern part of Bobani, was part of the "župa" (county) of Popovo (] ) which was located in the Hum province.
 The county bordered with Primorje county to the south, Trebinje area to the east, Dabar and Dubrave counties to the north, and Žaba county to the west.
 The Primorje county was later occupied by the Republic of Ragusa.
Park is an electoral ward of the Borough of Reading, in the English county of Berkshire.
 It is the far eastern ward and is bordered to its west by Abbey, Church and Redlands wards.
 On the north, east and south it is bordered by the civil parish of Earley in the Borough of Wokingham.
Kentwood is an electoral ward of the Borough of Reading, in the English county of Berkshire.
 It consists of the northern part of the suburb of Tilehurst, in the west of Reading, south of the River Thames.
 The ward is bordered by Mapledurham and Battle wards to the east, and Norcot and Tilehurst wards to the south.
 To the west the ward is bordered by the reduced civil parish of Tilehurst in the district of West Berkshire which is the remainder of the larger ancient parish, before the expansion of the Borough of Reading.
 The ward has schools and churches bearing a Tilehurst, rather than Reading name.