From the Wikipedia article :
A district of London, part of the London Borough of Lambeth. It is situated 1 mile (1.6 km) east of Charing Cross. The area is part of a business improvement district known as Waterloo Quarter, which includes The Cut and the Old Vic and Young Vic theatres, including some sections in the London Borough of Southwark.
The area was marshland towards the northern tip of the ancient parish of Lambeth. It was known as Lambeth Marshe, but was drained in the 18th century and is remembered in the Lower Marsh street name.
Waterloo is connected to the Strand area on the north bank of the River Thames by Waterloo Bridge. The first bridge on the site was opened in 1817 and the current bridge was opened in 1945. The bridge was named to commemorate the Battle of Waterloo in 1815. Waterloo Road also dates from this time, built on land belonging to the Archbishop of Canterbury. The Church of St John the Evangelist, Waterloo Road was constructed from 1822 by the Commissioners for Building New Churches as the population of the parish of Lambeth had significantly increased. After the opening of Waterloo railway station in 1848 the locality around the station and Lower Marsh became known as Waterloo.