 Horwood started his career with the Sheffield United youth system in July 2002, signing a three–year contract as a full-time scholar.After progressing the ranks of Sheffield United Academy and Reserves, Horwood joined Stockport County on a one-month loan on 10 March 2005.He then made his Stockport County debut two days later, on 12 March 2005, in a 2–1 loss against Colchester United.