Original: At one time, Newport Pagnell was one of the largest towns in the County of Buckinghamshire (the assizes of the County were occasionally held here) though today, despite its own substantial expansion, it has been completely dwarfed by the growth of Milton Keynes.
Simplified: At one time Newport Pagnell was one of the largest towns in the County of Buckinghamshire but today the new town of Milton Keynes has made it much less important.