Dallas County is in south-central Alabama, and was incorporated as a county in 1818. Some Dallas County public records will date back to this time but the majority of available documents are dated from 1908 when the state mandated that vital record information be kept.
When searching for records, you will have the greatest success at the county health department office in Selma. They issue certified copies of any vital records in the state database, even though issued outside of Dallas County itself. The office is open to the public, and you can just drop in during business hours to file a request. The forms are fairly simple, and will require identifying information (names, locations, dates) about the records you seek.
You also need to show your own ID, and pay the current search fee. The rate is $15 for the main types of vital records, except for the criminal records which will cost you $25 each. These fees are not refunded if they cannot locate the records you request (except with criminal backgrounds).
Dallas County Birth Records
Dallas County birth records are the most commonly requested, and they can be the hardest records to actually acquire. Privacy regulations limit their access to the person who is themselves on the record and their immediate family. Allowed relations are children, parents, siblings and current legal spouse. You won't be able to make a request for anyone else's records until 125 years after the date of birth. Most Dallas County birth records from before 1908 will not have the name of the child in the registration, so you must have accurate parent's names.
Dallas County Death Records
There are similar privacy restrictions on Dallas County death records, with only immediate family members allowed to get copies of the certificate. But the time frame for these restrictions is only 25 years. Any record older than 25 years can be accessed by anyone who wishes to make the request. Pre-1908 death records were very bare and may only have the name, date and location of death. Modern records have a great deal more information.
Dallas County Marriage Records
There are no privacy limits for Dallas County marriage records, so you are free to make requests for any documents you want. The main state collection of this sort of data started in 1936 though Probate courts usually have some sort of registration going back much farther. The courthouse in Selma may be able to help for any pre-1936 information you need.
Dallas County Criminal Records
At no time are Dallas County criminal records available to the general public. You are allowed to make a request for these documents for your own criminal background, but that is all. The records are kept by the state, so you have to send your request to the Alabama Criminal Justice Information Center. Their website has the forms and details. Some employers are permitted some access to criminal records in order to do background checks on employees. They are encouraged to use the Alabama Background Check secure website service for this, rather than order the documentation.