In the 17th century it was planned to move Ballymahon to Ballymulvey, with a new bridge spanning the river at the new location. These plans never materialized and the town remained at its present site. It is recorded in a mid-17th century survey that a large population resided in Castlecore surrounding a fortified castle or towerhouse and many houses lined the road from there through Moigh and into Ballymahon. Another castle or towerhouse stood on high ground beside the River Inny, where the local medical clinic stands today. These castles were mainly Farrell or Dillon strongholds.
Commerce and Industry in Ballymahon began to take on a more business like footing in the 18th century. Flax, corn, wheat and potatoes etc were plentiful due to the fertile growing conditions that prevailed locally. When the Royal Canal was ready in 1817, it marked the beginning of a booming and prosperous period in the town and hinterland. John Shuldham had constructed a flax mill in Ballymulvey; a corn mill was opened in 1839 by Henry Beven-Slator in Ballymahon beside the River Inny and other mills were built within a few kilometers of the town. It was hoped the railway would come through Ballymahon in the mid-19th century to continue boosting exports and growth, but it wasn’t accomplished and the decline began to set in.
The flax mill in Ballymulvey closed in 1870 and subsequently became a woollen mill which in turn closed in 1909. The other mills closed one by one in the early years of the 20th century – all had disappeared by 1920. There followed a somewhat depressed period, but following World War II economic recovery nationally, brought new growth and some mostly small industries back to Ballymahon. Today differs in that most people work in retail in the town; there is one fairly large employer along with a number of those small industries, while others travel to employment in neighbouring towns.