Complex sentence: The town was the administrative headquarters of the Borough of Oswestry until it was abolished on 1 April 2009 and is the third largest town in Shropshire, following Telford and Shrewsbury.
Split into simpler sentences: The town was the administrative headquarters of the Borough of Oswestry until that was abolished on 1 April 2009. Oswestry is the third largest town in Shropshire, following Telford and Shrewsbury.