Mass graves in Iraq have become well known since the US led invasion of Iraq toppled Saddam Hussein.
The following is taken from Fact Sheet – Bureau of Democracy, Human Rights and Labor and Bureau of Public Affairs
Mass graves in Iraq are characterized as unmarked sites containing at least six bodies. Some can be identified by mounds of earth piled above the ground or as deep pits that appear to have been filled. Some older graves are more difficult to identify, having been covered by vegetation and debris over time. Sites have been discovered in all regions of the country and contain members of every major religious and ethnic group in Iraq as well as foreign nationals, including Kuwaitis and Saudis. Over 250 sites have been reported, of which approximately 40 have been confirmed to date. Over one million Iraqis are believed to be missing in Iraq as a result of executions, wars and defections, of whom hundreds of thousands are thought to be in mass graves.
Most of the graves discovered to date correspond to one of five major atrocities perpetrated by the regime.
According to Kurdistan Regional Government in Iraq, about 85% of the mass graves in Iraq contain Iraqi Kurds, who were killed in a genocidal act just because of their ethnicity.
1- Az zubayr : Us military investigated mass grave of Iran-Iraq war casualties / CJTF-7 News / 5/6/2003
2- Abul khasim : Unconfirmed grave site near Abul Khasim, 20kms (13miles) south of Basra / BBC News / 5/9/2003
3- Abu Hasib : DART/APU visited site 20kms SE of Basra on may 17.HRW visited may 14. Locals report 1.000 / DART/APU Assessment / 5/17/2003
4- Basra : Locals disinterred over 125 corpses. many believed to be Shi’it Muslims executed in 1999 / DART cable- Kuwait 2259 / 5/12/2003
5- Ad Diwaniyah : DART visited site may 21. Twelve (12) corpses found in Ba ‘ath party security complex / BBC News / 5/28/2003
6- Najaf : Coalition reports 5 known mass graves in area. Locals disinterred. 500 corpses at site at makhazen. 20km from Shi’ite holy city / The Guardian / 5/12/2003 .
7- Amara : Up to 300 remains disinterred at a site 8kms outside of Amara. / DART/APU Assessment / 5/15/2003 .
8- Al hillah : DART/APU visited site 3 kms south of Al Hillah on may 3.Locals disinterred 50 sets of remains and estimate 500 remains from 1991. / Human Right watch / 5/5/2003 .
9- Imam Bakir : Locals discovered 40-50 victims from 1991 on may 2. HRW interviewed Locals / Associated press. Kuwait 2378 / 5/2/2003 .
10- Karbala : Locals excavated 45 remains on may 16. Human Rights Society in Karbala told DART there are 29 sites in area / DART Kuwait 2296 / 5/16/2003 .
11- Almusayyib : DART& ORHA Visited site NW of Al Musayyib. Babil on may 28.Over 600 corpses exhumed by may 28 and exhumations continue / Human Rights watch / 5/28/2003 .
12- Al mahawil : Over 600 victims from 1991 found at a clay pit and brick factory. Site visited by HRW on may 13 / Human Rights watch / 5/13/2003 .
13- Al mahawil : At nearby open field.2000- 3000 corpses exhumed. Locals estimate as many as 15,000.HRW Visited site on may 13. / BBC News / 5/13/2003
14- Salman Pak : Locals forced to bury more than 100 bodies in April 2003. Site visited by Us Army june7 / DART/APU Assessment / 6/7/2003 .
15- Radwaniyah : DART/APU visited Radwaniyah Prison site on may 13. not enough evidence to warrant more extensive investigation / Iraqi National Congress / 5/13/2003 .
16 Habbaniyeh : Mass grave of app. 600 kuwaiti POWs from 1991 war discovered by Iraqi National Congress. / DART/APU / 5/16/2003 .
17- Kirkuk : DART/APU visited may 9.. Locals estimate between 400 and 2000 corpses from 1991.Remains of 200 children found in Debs. / DART/APU / 5/9/2003 .
The 1983 attack against Kurdish citizens belonging to the Barzani tribe, 8,000 of whom were rounded up by the regime in northern Iraq and executed in deserts at great distances from their homes.
The 1988 Anfal campaign, during which as many as 182,000 Iraqi Kurds disappeared. Most of the men were separated from their families and were executed in deserts in the west and southwest of Iraq. The remains of some of their wives and children have also been found in mass graves.
Chemical attacks against Kurdish villages from 1986 to 1988, including the Halabja attack, when the Iraqi Air Force dropped sarin, VX and tabun chemical agents on the civilian population, killing 5,000 people immediately and causing long-term medical problems, related deaths, and birth defects among the progeny of thousands more.
The 1991 massacre of Iraqi Shia Muslims after the Shia uprising at the end of the Gulf war, in which tens of thousands of soldiers and civilians in such regions as Basra and Al-Hillah were killed.
A massacre of Kurds in 1991, which targeted civilians and soldiers who fought for autonomy in northern Iraq after the Gulf war, also resulted in mass graves.
Facts on the Fact Sheet appear to have been those gathered by US Senate committee investigations.
The remains of 113 Kurds, most of whom were women, children and teenagers, have been uncovered near Samawah.
Discovery of mass grave sites in Iraq has been done through the analysis of satellite imagery. This has 18 suspected sites, two of which are excavated having 28 and 10 adult males.
3,115 corpses uncovered in Mahaweel is one of the largest found (11/2003).
2,000 corpses found in Hillah.
Tony Blair has stated ‘We’ve already discovered, just so far, the remains of 400,000 people in mass graves.’ (11/03) The actual number of corpses found is closer to 5,000 (2004). 
The recovery of corpses is reported to be slow due to local violence and the need for identification of corpses, isolation of remains, forensics etc. Relatives have rushed to the graves in remembrance of missing relatives.