Thaddeus Kaliszewski, 88, of Ashland, passed away Thursday, May 5, after a short period of declining health. He was married for 45 years to the late Barbara (Freeman) Kaliszewski, who died in 2000. Born in Warsaw, Poland, Thaddeus immigrated to the U.S. in 1949 to attend Northeastern University, where he studied engineering, later earning his masters degree from Harvard University . Thaddeus retired from Mitre Corp. in Bedford where he worked for many years as an engineer. He was also employed as an engineer and researcher at General Electric, Sylvania, and Battelle Memorial Institute (Columbus, Ohio) over the years. As a graduate student he taught physics and mathematics at Harvard and later served as a faculty member at Worcester Polytechnic Institute. A resident of Ashland since 1975, he was a member of the Woodville Rod & Gun Club and very much enjoyed his hobby of target shooting, as well as his other hobby of computer programming. He is survived by three children: Suzanne May and her husband Tim of Hilliard, Ohio; Tom Kaliszewski and his wife Theresa of West Boylston; and Julia Shirley and her husband David of Somers, Conn.; as well as seven grandchildren: Kyle (Stephanie), Cory, and Caroline May; Thaddeus and Taylor Kaliszewski; and Alex and Alina Shirley. A graveside service will be held Friday, June 3rd, at 11:30 am in Wildwood Cemetery, Chestnut St. in Ashland.