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Despite the last name, the Reagan family not have a relation with Ronald Reagan, the famous actor in the 40s and 50s that eventually was elected two-term Governor of California and then the 40th President of the United States, serving from 1981 to 1989 (he was reelected to a second term in 1984).
Nearly each episode features a family dinner. This was at Tom Selleck's request to keep a sense of family. He also states that this scene is usually one of the longest ones to shoot. The family dinner happens always each Sunday around 17:00 to 17:30.
Although they play father and son, Len Cariou is only five years and four months older than Tom Selleck.
The actors who play Jack and Sean (Danny's kids) are brothers in real life in which Jack is the older brother and Sean the younger.
In Justice Served (2013) you can see that Jamie carries a picture of his late brother Joe tucked inside his police hat. This also appears to be the same picture of Joe that's shown in the beginning of the show's pilot episode on Frank's bureau while Frank is getting ready to attend Jamie's graduation from the Police Academy. The actor shown in the photo is uncredited.
The house (exterior) where the Reagan clan have their Sunday Dinner is located at 8070 Harbor View Terrace in Bay Ridge, Brooklyn (opposite the Verrazano Bridge). The house is situated in a cozy neighborhood near the water. Despite the fact that CBS uses its image for Blue Bloods, the estate is actually privately owned by a group of Catholics from the Middle East called the Maronites. Thus, this is not a place that is open to the public; anyone who wants to get a glimpse of it in real life will have to be respectful and cautious.