Businesses
- Imperial Hotel
- Imperial Russian Troupe of Dancers
- Imperial Tobacco Company of Great Britain and Ireland
- Independent Labour Party of Ireland
- Independent Newspapers Limited
- India Rubber Company
- Inniskeel Cooperative Agricultural Society Limited
- Inns of Court
- Institute of Shorthand Writers (Ireland)
- Invalid Requisites and Baby Carriage Company
- Ireland's Own
- Irish Agricultural Wholesale Society Limited
- Irish Bakery Engineering Company
- Irish Bleach Linen House
- Irish Church Missions
- Irish Club
- Irish Commercial Travellers' Association
- Irish Cooperative Agency Society Limited
- Irish Dairy Company
- Irish Direct Trading Company Limited
- Irish Gardeners' Association and Benevolent Society
- Irish Homestead Limited
- Irish Improved Roads Company
- Irish Industrial Printing and Publishing Company
- Irish Journalists' Association
- Irish Kinematograph Company Limited
- Irish National Foresters Brass and Reed Band
- Irish National Volunteers
- Irish Paper Mills Company Limited
- Irish Rugby Football Union
- Irish Shipowners' Company
- Irish Sub-Committee Post Office Relief Fund
- Irish Texts Society
- Irish Times Limited
- Irish Transport and General Workers' Approved Society
- Irish Transport and General Workers' Union
- Irish War Hospital Supply Depot
- Irish Wheelman Printing and Publishing Company Limited
- Isaac Braithwaite and Son, drysalter
- Islandbridge Mills
- Ivy Hotel