Mushrooms are very common in Ohio & Michigan lawns, usually there is no need to worry about them as they seldom do harm to our yards. Mushrooms in lawns typically are produced by decaying organic matter which may be buried under the soil or at the sub soil level, thatch can also aid in the development of mushroom production.
During periods of heavy rain (or irrigation), mushrooms may be more prevalent in the lawn as the organic matter speeds up the decomposition process. It may be lumber, old roots, buried branches or other organic material under the surface of the soil that is decaying and producing the mycelium which comes to the surface producing a mushroom. the mycelium feeds off of the buried material allowing for the break down and releasing nutrients into the lawn. Mushrooms can indicate a high level of nutrients in the yard and should not be thought of as a disease to the turf. They will not harm the grass (usually) and may be picked and discarded or left in the yard.