Early on in my research I found the immigration record of Pieter Koole. Nothing in any of the family stories gave me any indication any other relatives also came to the US. But after masses amounts of research tracing the lineage back in time, I started to search sideways - the siblings of my ancestors and even spouses families. Well, I'd always had some information on them, but not much. And, of course, someone had invented the Internet by now, and more and more information was available there. (Many Dutch record indexes are online, now more scanned records are going up.)
Well, surprise, surprise! Leendert Koole, brother of Pieter, also came to the US. Leendert was about 5 years younger and arrived with his wife in 1853, one year after Pieter and Tona arrived. Leendert also went to Kent County, Michigan where he was known as Leonard.
Indexes are wonderful things, but no match for the actual records. On the passenger list, next after Leendert and Willemijna, was listed Barend Koole - another brother. But the list also notes that Barend died aboard ship.
Just recently, doing some more searches with the online indexes, I found long after, in 1881, a nephew, Adriaan Koole, son of a fourth brother Cornelis, also came to the US. Adriaan traveled with a wife and 2 children. So far I have not found his family in the US.
By just 2 generations later no one in the family seems to have had any contact with these relatives. Pieter was my great-great grandfather, so Leendert was a great great grand uncle to me. Maybe one of these days I'll track his or Adriaan's descendants to find present days cousins.