There is an estimated population of 31 million crows in the US. In the US, the Migratory Bird Treaty Act of 1918, crows are a protected species. However, under this act, crows may be controlled without a federal permit when they are found, “committing or about to commit depredations upon ornamental or shade trees, agricultural crops, livestock or wildlife, or when concentrated in such numbers and manner to constitute a health hazard or other nuisance.”
You will need to consider your local and state laws before you take any type of control measures against crows.