16 July 1924: Eamon De Valera was released from captivity on this day. He had been held in Kilmainham Jail Dublin by the forces of the Irish Free State. He had been in detention since August 1923 after having been arrested in Ennis Co Clare at a political rally he was due to address in the General Election of that year.

‘Kilmainham Gaol opened in 1796 as the new County Gaol for Dublin. While most of the prisoners were common criminals, it also held political prisoners involved in Ireland’s struggle for independence. Included amongst those held here were Robert Emmet, Anne Devlin, the Fenians, Charles Stewart Parnell, Countess Markievicz and the leaders of the 1916 Easter Rising, 14 of whom were executed by firing squad in the Stonebreaker’s yard. The Gaol was closed in 1924 but was preserved as a national monument in the 1960s and restored by the Kilmainham Gaol Restoration Committee. It was handed over to the State in 1986 and today is run by the Office of Public Works.'

https://kilmainhamgaolmuseum.ie/

There were other Republican prisoners held in the jail too but De Valera was only allowed sporadic contact with them and did stints in solitary confinement. While there he thought over the events that had led him back into prison and pondered how he would go about breaking the Treaty and re establishing a Republican Party that was likely to be able gain the support of the Irish People.

....the immense crowds and the enthusiasm which everywhere greeted his appearance was a surprise even to the more optimistic Republicans who had believed that a long period of depression and defeatism had set in.

The Irish Republic, Chapter 90 by Dorothy Macardle

The day De Valera came out of there saw the start of his comeback in Irish Politics and led two years later to his break with Sinn Féin and the foundation of his own political Party - Fianna Fáil.