Columbus Delano, (June 4, 1809 - October 23, 1896) was a lawyer, rancher, banker, statesman and a member of the prominent Delano family. Delano was elected U.S. Congressman from Ohio, serving two full terms and one partial one. Prior to the American Civil War, Delano was a National Republican and then a Whig; as a Whig he was identified with the faction of the party that opposed the spread of slavery into the Western territories, and he became a Republican when the party was founded as the major anti-slavery party after the demise of the Whigs in the 1850s. During Reconstruction Delano advocated federal protection of African-Americans civil rights, and argued that the former Confederate states should be administered by the federal government, but were not part of the United States until they met the requirements for readmission to the Union.
Resignation and corruption (1875)
In 1875, Delano's reputation for personal honesty came under increasing scrutiny as revelations of corruption in the Grant administration continued to be the subject of investigations and media revelations. Westerners unhappy with Delano's rulings on land grants and other issues accused Delano's son John, an employee of the Interior Department, of corruption, bribery, and fraud. Governor Edward M. McCook of the Colorado Territory, claimed that John Delano had accepted a $1,200 bribe from a Colorado banker, Jerome B. Chaffee, to secure land patents from the Department of Interior.  The New-York Tribune reported that John Delano was profiteering through Interior's Office of the Surveyor General by accepting partnerships in Wyoming surveying contracts without having been trained in surveying or map making, and without providing any meaningful contribution to the fulfillment of the contracts; the obvious implication was John Delano had taken extortion money from illicit contract agreements. In March 1875, the former chief clerk of the Surveyor's Office, L. C. Stevens, wrote to Benjamin Bristow, Grant's Secretary of the Treasury, stating that Surveyor General Silas Reed had made several corrupt contracts which financially benefited John Delano. Stevens also said both Reed and John Delano had blackmailed five deputy surveyors for $5,000. More damaging was Stevens' charge that Columbus Delano knew and approved of what Reed had done for John Delano.  Both Bristow and Secretary of State Hamilton Fish demanded that Grant fire Delano. Grant declined, telling Fish, "If Delano were now to resign, it would be retreating under fire and be accepted as an admission of the charges." The controversy did not abate; by mid-August it became clear that Delano could not remain in office; Delano offered his resignation and Grant accepted, but Grant did not make it public. Grant finally announced his acceptance of Delano's resignation on October 19, 1875, after Bristow threatened to resign if Delano was not replaced. Grant replaced Delano with Zachariah Chandler, who quickly initiated civil service and other reforms in the Department of the Interior. Delano's administration was investigated by Congress, Chandler, and a special presidential commission; his personal conduct was exonerated, but his reputation as an honest, capable administrator was damaged, and Delano never again ran for office or served in an appointed one. In April 1876, The Committee on the Expeditures in the Interior Department confirmed that Reed had set up an illicit slush fund for John Delano's financial benefit, and that Delano thanked Reed while also telling him "to be careful to do nothing that would have the semblance of wrong."

Q: when did he resign?
A: 1875,

Q: wha did he resign from?
A: office;

Q: why did he resign?
A: Bristow threatened to resign if Delano was not replaced.
was he replaced?
Grant replaced Delano with Zachariah Chandler,
Grant replaced Delano with Zachariah Chandler,