Blodgett was born on January 10, 1898 in Schenectady, New York. She was the second child of Katharine Buchanan (Burr) and George Reddington Blodgett. Her father was a patent attorney at General Electric where he headed that department. He was shot and killed in his home by a burglar just before she was born. GE offered a $5,000 reward for the arrest and conviction of the killer,^[4] but the suspected killer hanged himself in his jail cell in Salem, New York.^[5] Her mother was financially secure after her husband's death,^{[citation needed]} and she moved to New York City with Katharine and her son George Jr. shortly after Katharine's birth. 

In 1901, Katherine's mother moved the family to France so that the children would be bilingual. They lived there for several years, returned to New York for a year, during which time Katherine attended school in Saranac Lake, then spent time traveling through Germany.^[6] In 1912, Blodgett returned to New York City with her family and attended New York City's Rayson School.

Blodgett's early childhood was split between New York and Europe, and she wasn't enrolled in school until she was eight years old.^[7] After attending Rayson School in New York City, she entered Bryn Mawr College on a scholarship, where she was inspired by two professors in particular: mathematician Charlotte Angas Scott and physicist James Barnes.^[7]

In 1917, Irving Langmuir, a former colleague of her father and future Nobel Prize laureate, took Katherine on a tour of General Electric (GE)'s research laboratories. He offered her a research position at GE if she first completed higher education, so she enrolled in a master's degree program at the University of Chicago after receiving her bachelor's degree.^[7]

At the University of Chicago she studied gas adsorption with Harvey B. Lemon,^[7] researching the chemical structure of gas masks.^[6] She graduated in 1918 and took a research scientist position working with Langmuir. After six years at the company, Blodgett decided to pursue a doctoral degree with hopes of advancing further within GE. Langmuir arranged for her to study physics at Cambridge University, at the Cavendish Laboratory persuading somewhat reluctant administrators to offer one of their few positions to a woman.^[6] She was enrolled at Newnham College, matriculating in 1924.^[8] She studied with Sir Ernest Rutherford and in 1926 became the first woman to receive a PhD in physics from Cambridge University.^[7]