You may have blue-eyed grass growing in your lawn. This is a May-to-June-blooming, native perennial that is widespread in Minnesota, especially in sandy soil areas. Despite the common name, blue-eyed grass is actually a member of the iris family. It is in the genus Sisyrinchium.

From your description of the purple flowers, it could be S. montana. The Prairie blue-eyed grass, S. campestre, usually has pale blue or white flowers. After the plant finishes blooming, pea-sized capsules form, which produce many tiny black seeds. When not blooming, the plants are often mistaken for grass. Although not often found in the typical garden store, companies that specialize in native plants will sometimes carry the plants and seeds. Now that you know the name, you can look it up in a wildflower book. There are two new books about Minnesota wildflowers we suggest you look for at the library. They are Stan Tekiela' s "Wildflowers of Minnesota" and Moyle's revised edition of "Northland Wildflowers."

It could also be Siberian squill or Scilla siberica. These commonly planted spring bulbs reseed abundantly and naturalize under favorable conditions.