In some cities and towns there are code enforcement officers who come by to check on complaints and check to make sure your yard is kept in good condition.
So if your grass remains uncut and grows out of control you can get a ticket or warning from the code enforcement officer.
Most times you'll just get a warning first to cut the grass and then if you don't cut the grass you can get a ticket or fine and the city might cut it for you for a pretty expensive fee.
If you cannot cut your own grass then you might need to hire someone to cut the grass and even a neighbor kid might cut your grass for a reasonable fee if you can't cut the grass yourself or you don't have the time to cut the grass.