What is a rain garden?
According to the Lake Simcoe Region Conservation Authority, each year in your yard there will be run off from rain and stormwater that will come from your roof, driveway and other hard surfaces. As the water moves toward the street (and sewer system) it can pick up a number of other substances (waste, salt, oils, etc) that can be harmful to water quality and aquatic habitat.
A rain garden is a much better use of the stormwater. A rain garden is a planted or stonecovered bed designed to receive stormwater and allow it to be slowly absorbed into the soil.
Rain gardens provide a good habitat for butterflies, birds and other wildlife and it requires little upkeep because it will contain native plants.
Parklane Landscapes has a great Rain Garden Calculator on their website that will help you determine the size of the rain garden you should create for your property.
For more information on creating a Rain Garden visit the Lake Simcoe Region Conservation Authority website.

Picture from LSRCA website.