Seeking info re Lars and Siri Marie Knutson

Would like background info re Lars Knutson (Knudsen), born Stavanger 1831. Wife Siri Marie born 27 Apr 1836 Stavanger. Son Johan born 13 Jan 1870. Emigrated about 1874 to Fillmore County, Minnesota. I realize Lars' name in Norway may have differed from the name I know. Four more children born in America, one of them Olava Sophia my grandmother, generally called Sophia.