Most willows like damp conditions. so look on damper, more open ground, such as near lakes, streams and canals. Some species like Goat willow can also be found growing in woodland, hedgerows and scrub.
For more info see https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/goat-willow/
There are six main species of willow (Salix) native to the UK. These are Bay, Crack, Goat, Grey, Osier and White Willow. Unfortunately, willows will easily hybridise (breed with another willow of a different species), so telling them apart can be quite tricky! When White and Crack willow hybridise, they make the Cricket Bat willow (used for making cricket bats, funnily enough!). They mainly grow in damp places. Some have long thin leaves (such as Crack and White willow) while other have broader leaves (Goat and Grey willow) and are commonly called sallows. Willows are dioecious which means that the male and female flowers (known as catkins) appear on separate trees. Goat and grey willow have silky grey male flowers often known as pussy willow because they look a little like a cat’s paw! Willows are pollinated by insects and produce large amounts of strong smelling nectar to attract them. Once fertilisation has taken place the white fluffy seeds are dispersed (spread) by the wind.
The painkiller, aspirin, first came from the chemical salacin, found in willow bark.
Have a look for willow trees in art and stories, they appear all over the place from the blue and white willow pattern china to the Whomping Willow in Harry Potter.