No one knows how many students William Merritt Chase taught, but they must have run into the thousands. He taught from around 1879, when he took his first student on, until well into the twentieth century, just a few years before he died.
Over that period, he had private students, the hundreds who flocked each summer to the Shinnecock Hills Summer School of plein air painting, and the large numbers who passed through the doors of some of the leading art schools of the day. The latter included his own Chase School of Art (which he opened in 1896), the Pennsylvania Academy of the Fine Arts, the Art Students League, and the Brooklyn Art Association.
Although in time Robert Henri and Chase fell out and went their separate ways, Henri was first invited by Chase into teaching, and they held one another in respect.
Here is a brief survey of twenty of Chase’s many students, whose subsequent careers we know about today. They are given in order of their year of birth.
Emma Lampert Cooper (1855-1920)
Attended the Art Students League in New York City before 1886, where she was taught by William Merritt Chase and Agnes Abbatt, and Cooper Union. In 1886 she travelled to Paris and the Netherlands for further study.

Silas Dustin (1855-1940)
He trained under Chase, and became the curator of the National Academy of Design. He was also an art dealer, and led the Biltmore Salon.
Dora Wheeler Keith (1857-1940)

She was taught by William Merritt Chase from 1879-1881, one of his first pupils, and he remained her mentor and friend. She went on to study at the Art Students League in New York, then spent two years at the Académie Julian in Paris.

Lydia Field Emmet (1866-1952)

With her older sister, attended the Académie Julian in Paris in 1884-5. They returned to New York to study with Chase and others, then returned to Paris to study under Bouguereau, Collin, and Tony Robert-Fleury. As her paintings remain in copyright, I offer Chase’s superb portrait of her.
Louise Upton Brumback (1867-1929)
First attended a Shinnecock Summer School in about 1900, then went to the New York School of Art and the Pennsylvania Academy of the Fine Arts.

John Marin (1870-1953)
He attended the Pennsylvania Academy of the Fine Arts in 1899-1901, where he studied under Thomas Pollock Anschutz and Chase, and at the Art Students League in New York. His work remains in copyright.
Edward Charles Volkert (1871-1935)
After studying at the Cincinnati Art Academy under Frank Duveneck, he was a student at the Art Students League in New York, under William Merritt Chase.

Ella Sophonisba Hergesheimer (1873-1943)
Attended the Pennsylvania Academy of Fine Arts, where she was taught by Cecilia Beaux and William Merritt Chase. In the summer of 1900, she attended Chase’s summer school in the Shinnecock Hills. As the best in her class at the Academy, she won the Cresson Travelling Scholarship, and studied at the Académie Colarossi in Paris for three years.

Kate Freeman Clark (1875-1957)
She was introduced to Chase when at the Art Students League in New York City, after 1895. Chase taught her still life painting, and remained her mentor for the rest of his life. He particularly respected her work, and had two of her paintings in his personal collection. Her work remains in copyright, and can be seen here.
Marsden Hartley (1877–1943)
Studied painting at the New York School of Art from about 1898, under Chase, then went on to the National Academy of Design.

Joseph Stella (1877-1946)
Having started to study medicine, he turned to art, at the Art Students League in 1897 and the New York School of Art from 1898 under Chase. He also attended a Shinnecock Summer School in 1901, taught by Chase. His paintings come out of copyright later this year.
M Jean McLane (1878-1964)
She studied in Cincinnati under Frank Duveneck, then in New York under Chase. Her work remains in copyright.
Edward Hopper (1882-1967)
He studied under Chase and Robert Henri at the New York School of Art from around 1900-1906, and his mature style was strongly influenced by Chase, Manet, and Degas. A major painter by any standard. His work remains in copyright.
Rockwell Kent (1882-1971)
After studying composition and design at the Art Students League in 1900, he learned to paint at the Shinnecock Summer Schools in 1900-1902, then in 1902 was a student of Robert Henri at the New York School of Art. A major painter by any standard. His work remains in copyright.
George Wesley Bellows (1882–1925)
Attended the New York School of Art from about 1904, mainly studying with Robert Henri. One of the school’s most distinguished alumni.

Julian Onderdonk (1882–1922)

Studied with Chase from 1901, initially at a Shinnecock Summer School, and a further two years after that. His father, Robert Jenkins Onderdonk (1852–1917) had earlier studied with Chase, and with James Carroll Beckwith.

Charles Henry Buckius Demuth (1883–1935).
From Drexel University, he went on to study at the Pennsylvania Academy of the Fine Arts, under William Merritt Chase. He travelled to Europe in 1907, studying at the Académies Colarossi and Julian in Paris.

Elizabeth Sparhawk-Jones (1885-1968)
She attended the Pennsylvania Academy of the Fine Arts from about 1901, where Chase was one of her teachers. He became her mentor, until his death in 1916, which affected her deeply. Her paintings remain in copyright.
Georgia O’Keeffe (1887-1986)
Probably Chase’s most eminent and popular former student, she studied under Chase at the Art Students League in New York City in 1907. The following year she won the League’s William Merritt Chase prize for still life. Her work remains in copyright. The Georgia O’Keeffe Museum holds more than a thousand of her works, and has a good online collection.
Leopold Gould Seyffert (1887-1956)
He studied at the Pennsylvania Academy of the Fine Arts in 1906-1913, where his teachers included Chase, Thomas Pollock Anschutz, and Cecilia Beaux. His work remains in copyright.
Additional articles:
Louise Upton Brumback (1867-1929)
George Wesley Bellows (1882–1925), up to 1914
George Wesley Bellows (1882–1925), after 1914
Marsden Hartley (1877-1943), 1 experiments to 1921
Marsden Hartley (1877-1943), 2 mature landscapes
Emma Lampert Cooper (1855-1920), the invisible wife
Edward Charles Volkert (1871-1935), the pastural painter
Ella Sophonisba Hergesheimer (1873-1943) and Dora Wheeler Keith (1857-1940)
Charles Demuth (1883–1935), Precisionism, and flowers
