Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Idaho, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, Wyoming
states and DC have abolished the death penalty
Alaska, Connecticut, Delaware, District of Columbia, Hawaii, Illinois, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New Mexico, New York, North Dakota, Rhode Island, Vermont, West Virginia, Wisconsin
I. History of Death Penalty Laws by State
The death penalty is legal in 31 states and illegal in 19 states (and DC). The "legal" and "illegal" designations in the "Death Penalty Status" column are based on the US Department of Justice's "Capital Punishment" reports. The June 29, 1972 Furman v. Georgia Supreme Court case placed a de facto moratorium on the death penalty in America. Many states amended their laws to comply with the mandates of the Furman decision and reinstate capital punishment.
As his last act as Governor, Winthrop Rockefeller granted clemency to all death-row inmates in 1970. Capital punishment was reinstated by legislature and Governor Bumpers in 1973. On June 22, 2012, the Arkansas Supreme Court ruled the death penalty law invalid until the state specifies the type and quantity of drug to be used for lethal injections.     
California Supreme Court case, People v. Anderson, temporarily ended capital punishment in 1972 but it was reinstated via voter approval of Proposition 17 in 1972. The Supreme Court of California again found the death penalty statute unconstitutional in 1976, but it was revised and reinstated in 1977.  
Capital punishment was abolished in 1897 and reinstated in 1901 by the legislature. Colorado was the last state to perform an execution (1967) before Furman. Capital punishment was reinstated post-Furman in 1975.  
Connecticut's capital punishment was reinstated post-Furman in 1976 and was abolished by legislature and Governor Malloy on Apr. 25, 2012. The 2012 repeal was not retroactive and death row inmates could still be executed. On Aug. 12, 2015, Connecticut's Supreme Court ruled the death penalty unconstitutional and banned any further executions.     
Capital punishment was abolished in 1958 and subsequently reinstated in 1961. It was reinstated post-Furman in 1974.   On Aug. 2, 2016, the Delaware Supreme Court ruled in the case Rauf v. State of Delaware that the state's death penalty statute violates the Sixth Amendment of the United States Constitution by giving judges too much leeway in sentencing.  On Dec. 15, 2016 the Delaware Supreme court ruled that their previous decision in Aug. should apply retroactively to the 12 men who were on Delaware’s death row. 
Capital punishment was reinstated post-Furman in 1972.   On Jan. 12, 2015, the US Supreme Court ruled that Florida’s method of sentencing people to death, which allowed judges, rather than juries, to impose a death sentence, violated the 6th Amendment. Florida Attorney General Pam Bondi said that due to the ruling, "the state will need to make changes to its death-sentencing statutes," and that "existing death sentences will need to be evaluated on a case-by-case basis." 
The death penalty was reinstated post-Furman in 1973. Georgia's capital punishment system received international attention with the 2011 execution of Troy Davis; Davis' supporters cited a lack of physical and DNA evidence.   
Illinois reinstated capital punishment post-Furman in 1974. Governor Ryan instituted a moratorium on executions on Jan. 31, 2000 and Governor Quinn signed legislation to abolish the death penalty on Mar. 9, 2011.  
Governor Carpenter abolished the death penalty in 1872. The legislature and Governor Gear reinstated capital punishment in 1878. Governor Hughes signed a death penalty abolition bill in 1965.    
The death penalty was reinstated post-Furman in 1978. In May 2001, Governor Glendening established a morotorium on executions which was lifted by his successor, Governor Ehrlich. [5, 14] Governor O’Malley signed legislation to abolish the death penalty on May 2, 2013. 
Capital punishment was reinstated by voter amendment in 1982 post-Furman. The law establishing capital punisment was ruled unconstitutional in 1984 with state court case Commonwealth v. Colon-Cruz.  
The voters of Nebraska reinstated the death penalty on Nov. 8, 2016.  The Nebraska Legislature had abolished the death penalty on May 27, 2015 with a 30-19 vote, overriding the veto of Governor Pete Ricketts. 
Capital punishment was reinstated in 1976 post-Furman. Governor Richardson signed abolition of the death penalty into law in 2009. The state still has a law allowing for execution for espionage, but the DOJ considers New Mexico to have no capital punishment.   
Capital punishment was reinstated by Governor Pataki in 1995 post-Furman, and New York's death penalty statute was ruled unconstitutional in 2004 in the state court's People v. Lavalle decision. The 2007 decision People v. Taylor also found part of the sentencing statute unconstitutional and declared that no defendants may be sentenced to death until the statute is corrected. Taylor’s sentence was converted to life in prison, and New York no longer had anyone on death row. Governor Paterson issued an executive order in 2008 to remove all capital punishment equipment from Green Haven Correctional Facility in 2008. The death penalty has not been abolished by law and may be used if the unconstitutional sentencing statute is revised by legislature.   
The Death Penalty Information Center, the Washington Post, and FindLaw have declared 2007 as the year New York’s death penalty was abolished. Other sources, including Assisting Lawyers for Justice (ALJ) on Death Row and Wikipedia, list the date as 2004.
Capital punishment ws abolished in 1915 for all crimes excluding treason and murder committed by already jailed inmates. In 1973 the legislature voted to make no crimes eligible for the death penalty.  
Capital punishment was abolished in 1914 by a public vote and reinstated in 1920 at the urging of Governor West. In 1964 Oregon voted to abolish the death penalty and in 1978 voted to reinstate capital punishment. A 1981 state Supreme Court Case ruled the 1978 measure unconstitutional, and in 1984 voters approved a measure that overturned the 1978 decision making the death penalty legal again. In 2011 Governor Kitzhaber placed a moratorium on executions.     
A 1972 state Supreme Court case (Commonwealth v. Bradley) ruled Pennsylvania's application of capital punishment unconstitutional. The legislature reinstated the death penalty in 1974, only to have the State Supreme court rule its reinstatement unconstitutional in 1977. In 1978 the legislature passed an edited death penalty bill to correct the constitutional concerns raised by the state Supreme Court and the US Supreme Court.   On Feb. 13, 2015, Pennsylvania Governor Tom Wolf declared a death penalty moratorium in the state. 
Capital punishment was abolished in 1852 and reinstated by legislature in 1873. After Furman, the state rewrote its death penalty law to mandate capital punishment for certain crimes. That mandate was ruled unconstitutional in 1979. In 1984 the legislature abolished capital punishment entirely.  
The legislature effectively abolished capital punishment in 1965 unless a warden, prison employee, or law enforcement officer was murdered. But Vermont's jurors never used the death sentence option when available so legislators removed that exception in 1987. Vermont law still allows for execution for treason but the DOJ considers Vermont to have no capital punishment.     
Capital punishment was reinstated post-Furman in 1977.  
II. Timeline of State Death Penalty Laws, 1972-2016
Notes and Sources:
The chart above shows the reinstatement or abolishment of the death penalty at the end of the specified calendar year, Dec. 31.
The following 10 states declared capital punishment illegal before the June 29, 1972 Furman v. Georgia ruling and have not changed their laws: Alaska (1957), Hawaii (1957), Iowa (1965), Maine (1887), Michigan (1846 except for treason; 1963 for all crimes), Minnesota (1911), North Dakota (1915 except for treason and murder by inmates; 1973 for all crimes), Vermont (1965 except murder of correctional officer; 1987, except treason), West Virginia (1965), and Wisconsin (1853).
Washington, DC is not included in the chart above. DC reenacted the death penalty in 1973, but it was repealed by the DC Council in 1981.
New York has declared portions of the state death penalty laws unconstitutional, and Oregon's Governor West placed a moratorium on state executions in 2011. The Department of Justice includes these two states in its "Capital Punishment" reports because the death penalty laws have not been abolished or repealed so the states remain listed as having legal capital punishment.
David Ariosto, "Connecticut Becomes 17th State to Abolish Death Penalty," www.cnn.com, Apr. 25, 2012
Arizona Attorney General, "Capital Punishment in Arizona," www.azag.gov (accessed July 20, 2012)
Robbie Brown, "Arkansas Upends Death Penalty," www.nytimes.com, June 22, 2012
Jonathan J. Cooper, "John Kitzhaber, Oregon Governor, Imposes Moratorium on Death Penalty for Rest of His Term," www.huffingtonpost.com, Nov. 22, 2011
Death Penalty Information Center, "Death Penalty Information by State," www.deathpenaltyinfo.org (accessed July 18, 2012)
Encyclopedia of Arkansas History & Culture, "Capital Punishment," www.encyclopediaofarkansas.net (accessed July 20, 2012)
Iowans Against the Death Penalty, "Iowa," www.iadp.org (accessed July 20, 2012)
Michael Kirk, "The History of the Death Penalty in Connecticut," www.today.uconn.edu, Oct. 24, 2011
Kathleen A. O'Shea, Women and the Death Penalty in the United States, 1900-1998, 1999
Michael H. Reggio, "Frontline, the Execution: History of the Death Penalty," www.pbs.org (accessed July 20, 2012)
Wilson Ring, "Vt. Prosecutors May Seek Death Penalty in Abduction," www.Boston.com, July 6, 2008
South Dakota Department of Corrections, "Frequent Questions: Capital Punishment" www.doc.sd.gov (accessed July 20, 2012)
Texas Execution Information Center, "Texas Execution Information Center Execution Reports," www.txexecutions.org (accessed July 20, 2012)
US Department of Justice (USDOJ) US Bureau of Justice Statistics (USBJS), "Publications & Products: Capital Punishment," bjs.ojp.usdoj.gov (accessed July 18, 2012)
William Yardley, "Oregon Governor Says He Will Block Executions," www.nytimes.com, Nov. 22, 2011
Joe Sutton, "Maryland Governor Signs Death Penalty Repeal," cnn.com, May 2, 2013
Julie Bosman, "Nebraska Abolishes the Death Penalty," nytimes.com, May 27, 2015
CNN, "Pennsylvania Governor Halts Death Penalty While 'Error Prone' System Reviewed," cnn.com, Feb. 14, 2015
Reuters, "Connecticut's Top Court Bans Death Penalty in State," reuters.com, Aug. 13, 2015
Whitney Ray, "Attorney General Bondi’s Statement on Today’s US Supreme Court Ruling,” myfloridalegal.com, Jan. 12, 2016
Eyder Peralta, "Delaware Supreme Court Finds State's Death Penalty Law Is Unconstitutional," npr.org, Aug. 2, 2016
New York Times, "With Death Penalty Back, Nebraska Looks Ahead to Executions,” nytimes.com, Nov. 9, 2016
Jessica Masulli Reyes, "Supreme Court: Executions off for Those on Death Row,” delawareonline.com, Dec. 15, 2016
IV. Related Resources
Death Row Inmates, 1953-2009 - Read the number of death row inmates, executions, and average time in prison, as well as the primary reasons for removal from death row.
US Executions 1608-2002 - ProCon.org created summary graphs and charts using data from M. Watt Espy, Jr. and John Ortiz Smykla’s 32-year study of 15,269 executions performed from 1608-2002 under legal civil authority in the United States, or within territories which later became part of the United States.