I can't find my family...Olsen and Morset

I have a birth certificate listing my great grandparents as Sarah Olsen or Olson, born around 1880 in Norway and Liebert Morset born around 1874 in Norway. I don't have any other information on them except that at the time of my great grandmothers birth, she was thier eleventh child and Liebert was a Pastor. I have an address on the birth certificate that shows she was born at home, but when I go to that address in Chicago on the census, there is an Italian family living there! I am at a loss. What can these names be? I can't find them anywhere. Thanks for any help. Lori