The ordnance survey website. osi.ie has a web browser that enables you to look att he 1840s coloured maps which have the parishs marked. It cost by blocks f three days or a month or a year, and for an extra fee you can download the maps.
For townlands and I think parish lists see seanruad.com
Don’t be tempted to pay to see Lewis Directory on the OSI webiste, – its free elsewhere.