Do I need a visa for Paris, if my connecting flight stops for 24 hours in Paris?

If you plan to enter the country (France in this case) then you require visa before travel (embassy advises minimum of 15 days before travel)

France Visa Application Centres

For Non-Professional Travel (family visit, private visit, tourists)

Is applicable in case you are traveling to visit your friends/relatives. This visa is given for travel of less than 90 days. Visa fee: 60 euros

Mandatory Documents:

Original passport valid for at least six months with minimum 2 blank pages. (face to face)
+ 1 photocopy of passport first page. The passport should be issued less than 10 years ago.
The photocopy of Passport photo page and address page of the applicant.
Photocopies of all valid US, U.K. and previous Schengen visas.
One application form & undertaking form with all columns filled in and 2 recent photographs in the size of 3.5 cms x 4.5 cms with white / light background.
    ALL APPLICANTS SHOULD MENTION THEIR MOBILE NUMBER ON THE VISA APPLICATION FORM.
    TRAVEL AGENTS AUTHORIZED BY THE EMBASSY OF FRANCE MUST MENTION THE APPLICANTS MOBILE NUMBER ON THE VISA APPLICATION FORM AND NOT THEIR OWN MOBILE NUMBER OR TRAVEL AGENCY NUMBER.
Covering letter IN ORIGINAL signed by the applicant. For self employed/ businessman, going on tourist visa, covering letter preferably on company's letterhead is required
Copy of CONFIRMED prepaid hotel reservation OR sponsorship certificate (attestation d'accueil & photo id proof of invitee*) IN ORIGINAL
Copy of ITINERARY prepared by the travel agency (for those going on tour)
Copy of income tax papers of last one year, last THREE month bank statement & updated, last 3 months salary slips
Photocopy of OVERSEAS medical insurance policy + REPATRIATION, evacuation cover (equivalent to 30,000 euros). Insurance should have the validity for at least 10-15days more after the return to India . Please carry your original insurance for verification at the time of submission of visa application form. **
Copy of air ticket or PNR (booking printout).
All applicants except first time traveler (traveling first time to a Schengen country) while applying for a French visa will be required to fill visa insurance undertaking form in addition to the visa application form.
For minor travelling alone the visa application must include an authorization from both his/her parents to travel alone. The authorization has to be certified by an entitled Indian authority and enclose copy of the parents' identity.

If the minor is travelling with an adult other than his/her parents, this adult has to be legally authorized by the minor's parents to accompany him/her and take any measure that be needed in case of illness, accident,etc.

If the minor is accompanied by only one of his/her parents, the other one should give his/her legal authorization to let her/his child travelling with his/her spouse.

For any student under 18, applicants are requested by the French authorities to provide with either a photocopy of certificate from their school or university or any other document as a proof of their enrollment as a student or apprentice.
The photocopy of certificate from school or university or any other proof of professional or educative occupation is also requested whenever a young person over 18 is depending on his parents for his/her living expenses
Domestic help at the private service of a foreign national or a French national, accompanying his employer to France for a short stay needs to hold a working permit, like any foreigner going to work, full time or part time, in France.

Submission of a contract established between the employee and the employer in accordance with the French Labour law, approved by the DDTEFP( Direction du travail, de l’emploiet de la formation professionnelle) center of the employer’s place of vacation is compulsory for application for a visa.
NOC for school, college or Employers is required as a mandatory document. NOC from spouse with a signature proof if any one of the couple is traveling for tourism purpose.
Marriage certificate is mandatory for all the applicants who are married if their spouse name is not endorsed in the passport. If someone is not having a marriage certificate (newly married couple) then an affidavit declaring the applicants to be married with their photos pasted on the same should be produced.
All child within the age of 18years should provide a copy of birth certificate as a mandatory document.

The documents must be arranged in the order given above.

• Attestation d'accueil (sponsorship certificate) can be obtained in any city from the local town hall in France. **Please note that original insurance will be seen by the submission officer at the time of submission of visa application form. Online insurance should be certified by the insurance company.Also from 01st November 2007 onwards insurance should cover minimum 30 days even if applicant stay duration in France is less than 30 days.

(I am presuming you are referring to Paris Charles De Gaulle/CDG airport and not Paris Orly/ORY which has different rules. I'm also presuming that you are not connecting to a flight going via another Schengen countries, as this will also change the requirements)

As an Indian Citizen, with a US visa and on the way to/from the US you are able to "Transit Without Visa" (TWOV) through CDG, as long as your stay in the country is no more than exactly 24 hours (based on schedules landing and departure times of your flights). If your stay is even 1 minute more than 24 hours then you will NOT be able to use TWOV.

TWOV does NOT allow you to pass through passport control (ie, immigration), and thus does not allow you to leave the airport. You will need to remain airside for the entire duration of your layover.

If your stay is more than 24 hours, or if you want to leave the airport, then you will need to apply for a France/Schengen "Short Stay" visa.