Complex sentence: Minnesota is well known for its large population of Swedish immigrants, and Swedes have been getting together since 1934 to hold the "Svenskarnas Dag" (Swedish Heritage Day) at the park in June of each year.
Split into simpler sentences: Minnesota is well known for its large population of Swedish immigrants. Since 1934 Swedes have celebrated "Svenskarnas Dag" (Swedish Heritage Day) at the park in June of each year.